Holmes soon filed a patent application for "Medical device for analyte monitoring and drug delivery," a wearable device that would administer medication, monitor patients' blood, and adjust the dosage as needed.
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However, Draeger says its device only picks up on Delta 9 Tetrahydrocanibol, the active analyte in THC that causes impairment, which stays in a person's system for four to six hours.
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Andreescu's paper test can measure different toxins, and the intensity of the colors that come up on the sensors indicate the concentration of the analyte, which indicates spoilage or other factors.
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This is easier than most of the other paper sensors being developed, and, practically speaking, means that users wouldn't have to add any other chemicals to the test—just the analyte they wish to measure.
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Then based on its response and its response time, we are able to calculate how much of that particular analyte is in the sample—based on percent by weight or milligrams per gram, based on how the math is done.
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In a competitive, homogeneous immunoassay, unlabelled analyte in a sample competes with labelled analyte to bind an antibody. The amount of labelled, unbound analyte is then measured. In theory, the more analyte in the sample, the more labelled analyte gets displaced and then measured; hence, the amount of labelled, unbound analyte is proportional to the amount of analyte in the sample. Two-site, noncompetitive immunoassays usually consist of an analyte "sandwiched" between two antibodies.
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As in a competitive, homogeneous immunoassay, unlabelled analyte in a sample competes with labelled analyte to bind an antibody. In the heterogeneous assays, the labelled, unbound analyte is separated or washed away, and the remaining labelled, bound analyte is measured.
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The analyte-enzyme-fragment-conjugate is still able to reassemble with the other enzyme fragment to form an active enzyme. However it is unable to do this if the analyte is bound to an antibody. To determine the quantity of analyte in a sample, an aliquot of sample must be added to a solution containing enzyme-fragment-analyte-conjugate, the other enzyme fragment, antibody directed against the analyte and substrate for the enzyme reaction. Competition for the antibody occurs between the analyte in the sample and the enzyme-fragment-analyte-conjugate.
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The matrix is then thought to transfer proton to the analyte molecules (e.g., protein molecules), thus charging the analyte.
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In some chemiresistors the resistance changes simply indicate the presence of analyte. In others, the resistance changes are proportional to the amount of analyte present; this allows for the amount of analyte present to be measured.
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The analyte in the unknown sample is bound to the antibody site, then the labelled antibody is bound to the analyte. The amount of labelled antibody on the site is then measured. It will be directly proportional to the concentration of the analyte because the labelled antibody will not bind if the analyte is not present in the unknown sample. This type of immunoassay is also known as a sandwich assay as the analyte is "sandwiched" between two antibodies.
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High concentrations of analyte in the sample lead to a relatively small amount of the enzyme- fragment-analyte-conjugate being prevented from forming active enzyme and therefore high enzyme activity. Conversely, low concentrations of analyte in the sample lead to a relatively large amount of the enzyme-fragment-analyte- conjugate being prevented from forming active enzymes and therefore low enzyme activity.
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The area under a peak is proportional to the amount of analyte present in the chromatogram. By calculating the area of the peak using the mathematical function of integration, the concentration of an analyte in the original sample can be determined. Concentration can be calculated using a calibration curve created by finding the response for a series of concentrations of analyte, or by determining the relative response factor of an analyte. The relative response factor is the expected ratio of an analyte to an internal standard (or external standard) and is calculated by finding the response of a known amount of analyte and a constant amount of internal standard (a chemical added to the sample at a constant concentration, with a distinct retention time to the analyte).
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Competitive assays are generally used for smaller analytes since smaller analytes have fewer binding sites. The sample first encounters antibodies to the target analyte labelled with a visual tag (colored particles). The test line contains the target analyte fixed to the surface. When the target analyte is absent from the sample, unbound antibody will bind to these fixed analyte molecules, meaning that a visual marker will show.
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Through a microflow system, a solution with the prey analyte is injected over the bait layer. As the prey analyte binds the bait ligand, an increase in SPR signal (expressed in response units, RU) is observed. After desired association time, a solution without the prey analyte (usually the buffer) is injected on the microfluidics that dissociates the bound complex between bait ligand and prey analyte. Now as the prey analyte dissociates from the bait ligand, a decrease in SPR signal (expressed in resonance units, RU) is observed.
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Once the charge is neutralized, the electrostatic interaction between the analyte and the stationary phase no longer exists and the analyte will elute from the cartridge.
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Conversely, when the target analyte is present in the sample, it binds to the antibodies to prevent them binding to the fixed analyte in the test line, and thus no visual marker shows. This differs from sandwich assays in that no band means the analyte is present.
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The utility of cyclic voltammetry is highly dependent on the analyte being studied. The analyte has to be redox active within the potential window to be scanned.
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The last step for the FluoroSpot assay is to analyze the fluorophores under an automated fluorescence reader that has separate filters for the different fluorophores being analyzed. These filters should be selected for the specific wavelengths of the fluorophores if you want accurate measurements. Since the FluoroSpot assay identifies and quantifies the presence of multiple analytes, it is possible that the absorption of one analyte can affect the secretion of another analyte; this is called capture effects. The affect an analyte has on another analyte could be positive or negative (the production of the second analyte can either increase or decrease).
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Elution then is the process of removing analytes from the adsorbent by running a solvent, called an "eluent", past the adsorbent/analyte complex. As the solvent molecules "elute", or travel down through the chromatography column, they can either pass by the adsorbent/analyte complex or they can displace the analyte by binding to the adsorbent in its place. After the solvent molecules displace the analyte, the analyte can be carried out of the column for analysis. This is why as the mobile phase passes out of the column, it typically flows into a detector or is collected for compositional analysis.
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Flow-induced dispersion analysis (FIDA) is an immobilization-free technology used for characterization and quantification of biomolecular interaction and protein concentration under native conditions. In the FIDA assay, the size of a ligand (indicator) with affinity to the target analyte is measured. When the indicator interacts with the analyte the apparent size increases and this change in size can be used to determine the analyte concentration and interaction. Additionally, the hydrodynamic radius of the analyte-indicator complex is obtained.
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The relative magnitude of the signals quantitatively reveals the enantiomeric purity of the analyte. Also, a model of the solvated complex may be used to deduce absolute configuration of an enantioenriched analyte.
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The analyte associates with and is retained by the polar stationary phase. Adsorption strengths increase with increased analyte polarity. The interaction strength depends not only on the functional groups present in the structure of the analyte molecule, but also on steric factors. The effect of steric hindrance on interaction strength allows this method to resolve (separate) structural isomers.
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ARS excites multiple normal modes by sweeping the excitation frequency of an analyte with no internal vibrations to obtain a resonance spectrum. These resonance frequencies greatly depend on the type of analyte being measured and also depend greatly on the physical properties of the analyte itself (mass, shape, size, etc.). The physical properties will greatly influence the range of frequencies produced by the resonating analyte. In general small analytes have megahertz frequencies while larger analytes can be only a few hundred hertz.
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This change in current (or conductance) can be measured, thus the binding of the analyte can be detected. The precise relationship between the current and analyte concentration depends upon the region of transistor operation.
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Major disadvantages include time-consuming sample preparation and inefficient analyte ionization.
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The more complex the analyte the more complex the resonance spectrum.
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Sandwich assays are generally used for larger analytes because they tend to have multiple binding sites. As the sample migrates through the assay it first encounters a conjugate, which is an antibody specific to the target analyte labelled with a visual tag, usually colloidal gold. The antibodies bind to the target analyte within the sample and migrate together until they reach the test line. The test line also contains immobilized antibodies specific to the target analyte, which bind to the migrated analyte bound conjugate molecules.
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This limits the precision of direct amperometry. If the potential applied to the working electrode is sufficient to reduce the analyte, then the concentration of analyte close to the working electrode will decrease. More of the analyte will slowly diffuse into the volume of solution close to the working electrode, restoring the concentration. If the potential applied to the working electrode is great enough (an overpotential), then the concentration of analyte next to the working electrode will depend entirely on the rate of diffusion.
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There are two main types of vibrations: free and forced. Free vibrations are the natural or normal modes of vibration for a substance. Forced vibrations are caused by some sort of excitation to make the analyte resonate beyond its normal modes. ARS employs forced vibrations upon the analyte unlike most commonly used techniques which use free vibrations to measure the analyte.
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The matrix must absorb at the laser wavelength and ionize the analyte. Matrix selection and solvent system relies heavily upon the analyte class desired in imaging. The analyte must be soluble in the solvent in order to mix and recrystallize the matrix. The matrix must have a homogeneous coating in order to increase sensitivity, intensity, and shot-to- shot reproducibility.
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In other words, the "sandwich" quantify antigens (i.e. biomolecules) between two layers of antibodies (i.e. capture and detection antibody). For the competitive assay technique, unlabeled analyte displaces bound labelled analyte, which is then detected or measured.
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Keepers are substances (typically solvents, but sometimes adsorbent solids) added in relatively small quantities during an evaporative procedure in analytical chemistry, such as concentration of an analyte-solvent mixture by rotary evaporation. The purpose of a keeper is to reduce losses of a target analyte during the procedure. Keepers typically have reduced volatility and are added to a more volatile solvent. In the case of volatile target analytes, it is difficult to totally avoid loss of the analyte in an evaporative procedure, but the presence of a keeper solvent or solid is intended to preferentially solvate or adsorb the analyte, so that the volatility of the analyte is reduced as the evaporative procedure continues.
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The competitive hybridization assay is similar to a traditional competitive immunoassay. Like other hybridization assays, it relies on complementarity, where the capture probe competes between the analyte and the tracer–a labelled oligonucleotide analog to the analyte.
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Diagram of GCMS. The diagram shows the pathway of the analyte. The analyte first passes through the gas chromatographer and then the separated analytes are subjected to mass analysis. Different types of mass analyzers, ToF, qudrupole, etc.
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The selection of a matrix is the first step when preparing samples for MALDI analysis. The primary goals of the matrix are to absorb the energy from a laser, thus transferring it to the analyte molecules, and to separate the analyte molecules from each other. A consideration that should be taken into account when choosing a matrix is what type of analyte ion is expected or desired. Knowing the acidity or basicity of the analyte molecule compared with the acidity or basicity of the matrix, for example, is valuable knowledge when choosing a matrix.
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The unknown analyte in the sample binds with labelled antibodies. The unbound, labelled antibodies are washed away, and the bound, labelled antibodies are measured. The intensity of the signal is directly proportional to the amount of unknown analyte.
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The current produced is a direct measure of the rate of electron transfer. The current reflects the reaction occurring between the bioreceptor molecule and analyte and is limited by the mass transport rate of the analyte to the electrode.
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To counteract capture effects, it is possible to use co-stimulation in order to bypass the decreased production of an analyte. This is when a second antibody that stimulates the production of the same analyte is added to the wells.
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The specific binding capabilities and catalytic activity of enzymes make them popular bioreceptors. Analyte recognition is enabled through several possible mechanisms: 1) the enzyme converting the analyte into a product that is sensor-detectable, 2) detecting enzyme inhibition or activation by the analyte, or 3) monitoring modification of enzyme properties resulting from interaction with the analyte. The main reasons for the common use of enzymes in biosensors are: 1) ability to catalyze a large number of reactions; 2) potential to detect a group of analytes (substrates, products, inhibitors, and modulators of the catalytic activity); and 3) suitability with several different transduction methods for detecting the analyte. Notably, since enzymes are not consumed in reactions, the biosensor can easily be used continuously.
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In electrospray ionization, a liquid is pushed through a very small, charged and usually metal, capillary. This liquid contains the substance to be studied, the analyte, dissolved in a large amount of solvent, which is usually much more volatile than the analyte. Volatile acids, bases or buffers are often added to this solution too. The analyte exists as an ion in solution either in its anion or cation form.
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Secondary processes involve ion- molecule reactions to form analyte ions. In the lucky survivor model, positive ions can be formed from highly charged clusters produced during break-up of the matrix- and analyte-containing solid. The lucky survivor model (cluster ionization mechanism) postulates that analyte molecules are incorporated in the matrix maintaining the charge state from solution. Ion formation occurs through charge separation upon fragmentation of laser ablated clusters.
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The use of a calibrator is often employed in immunoassays. Calibrators are solutions that are known to contain the analyte in question, and the concentration of that analyte is generally known. Comparison of an assay's response to a real sample against the assay's response produced by the calibrators makes it possible to interpret the signal strength in terms of the presence or concentration of analyte in the sample.
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The volume of titrant that reacted with the analyte is termed the titration volume.
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RP-HPLC allows the measurement of these interactive forces. The binding of the analyte to the stationary phase is proportional to the contact surface area around the non-polar segment of the analyte molecule upon association with the ligand on the stationary phase. This solvophobic effect is dominated by the force of water for "cavity- reduction" around the analyte and the C18-chain versus the complex of both. The energy released in this process is proportional to the surface tension of the eluent (water: 7.3 J/cm², methanol: 2.2 J/cm²) and to the hydrophobic surface of the analyte and the ligand respectively.
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In such a case, the current is said to be diffusion limited. As the analyte is reduced at the working electrode, the concentration of the analyte in the whole solution will very slowly decrease; this depends on the size of the working electrode compared to the volume of the solution. What happens if some other species which reacts with the analyte (the titrant) is added? (For instance, chromate ions can be added to oxidize lead ions.) After a small quantity of the titrant (chromate) is added, the concentration of the analyte (lead) has decreased due to the reaction with chromate.
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From the increase in the peak area (or peak height), the original concentration can be computed by extrapolation. The detector response must be a linear function of analyte concentration and yield no signal (other than background) at zero concentration of the analyte.
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In a competitive, homogeneous immunoassay unlabeled analyte displaces bound labelled analyte, which is then detected or measured. Immunoassays can be run in a number of different formats. Generally, an immunoassay will fall into one of several categories depending on how it is run.
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Response factor, usually in chromatography and spectroscopy, is the ratio between a signal produced by an analyte, and the quantity of analyte which produces the signal. Ideally, and for easy computation, this ratio is unity (one). In real-world scenarios, this is often not the case.
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C. Parameshwara Murthy. New Age International, 2008. . p.632 It involves two steps, namely the titration of the analyte with potassium permanganate solution and then the standardization of potassium permanganate solution with standard sodium oxalate solution. The titration involves volumetric manipulations to prepare the analyte solutions.
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In a typical BioFET, an electrically and chemically insulating layer (e.g. Silica) separates the analyte solution from the semiconducting device. A polymer layer, most commonly APTES, is used to chemically link the surface to a receptor which is specific to the analyte (e.g. biotin or an antibody).
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The main use of these tips are to flow samples through and the analytes affinity for the bound antigen/antibody allows for the capture of analyte. Non specifically bound compounds are rinsed out of the MSIA tips. The process can be simplified into 6 simple steps which Thermo termed the "work flow". #Gather Sample #Load Affinity Ligand #Purify Target Analyte #Elute Target Analyte #Pre-MS Sampling Process #MS Analysis Many "work flows" are commercially available for purchase.
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A ChemFET is a chemically-sensitive field-effect transistor, that is a field- effect transistor used as a sensor for measuring chemical concentrations in solution. When the target analyte concentration changes, the current through the transistor will change accordingly. Here, the analyte solution separates the source and gate electrodes. A concentration gradient between the solution and the gate electrode arises due to a semi-permeable membrane on the FET surface containing receptor moieties that preferentially bind the target analyte.
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Communiqué: A Mayo Reference Services Publication. 2003; 28(3):1–4. So-called 'sandwich' immunoassays are particularly susceptible to this interference. (Sandwich immunoassay = two- site, noncompetitive immunoassays in which the analyte in the unknown sample is bound to the antibody site, then labeled antibody is bound to the analyte.
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As mentioned above, as the matrix is depleted, the ionization decreases as well, so maintaining the matrix is vital. Thirdly, the matrix should not react with the solid analyte in question, or if it does react, it should be in an understood and reproducible way. This ensures reproducibility of analysis and identification of the actual analyte rather than a derivative of the analyte. The most commonly used compounds as a matrix are variations of glycerol, such as glycerol, deuteroglycerol, thioglycerol, and aminoglycerol.
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It has numerous advantages over the other techniques used. It is a sensitive and selective analytical method, making it ideal for the analysis of complex samples and those with low analyte concentrations. The method is also beneficial in that it provides important structural information on the analyte which is helpful for aiding analyte identification and when unknown analytes are present in the sample. The technique has benefits over LC-FLD as the derivatisation and purification extraction steps are not necessary.
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Alternatively, if the analyte itself is an antibody, its target antigen can be used as the binding reagent.
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Example: An ion-selective electrode might be calibrated using dilute solutions of the analyte in distilled water. If this calibration is used to calculate the concentration of the analyte in sea water (high ionic strength), significant error is introduced by the difference between the activity of the analyte in the dilute solutions and the concentrated sample. This can be avoided by adding a small amount of ionic-strength buffer to the standards, so that the activity coefficients match more closely. Adding a TISAB buffer to increase the ionic strength of the solution helps to "fix" the ionic strength at a stable level, making a linear correlation between the logarithm of the concentration of analyte and the measured voltage.
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For maximum sensitivity, the sample should form a perfect monolayer at the surface of a substrate having low volatility. This monolayer effect can be seen in that once a certain concentration of analyte in matrix is reached, any concentration above that is seen to exhibit no effect, because once the monlayer is formed, any additional analyte is beneath the monolayer, and thus not affected by the atom beam. The concentration needed to cause this effect is seen to change as the amount of non-volatile matrix changes. So concentration of solid analyte needs to be considered in the preparation of the solution for analysis so that signal from "hidden" analyte is not missed.
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During retrodialysis, the microdialysis probe is perfused with an analyte-containing solution and the disappearance of drug from the probe is monitored. The recovery for this method can be computed as the ratio of drug lost during passage (Cin−Cout) and drug entering the microdialysis probe (Cin). In principle, retrodialysis can be performed using either the analyte itself (retrodialysis by drug) or a reference compound (retrodialysis by calibrator) that closely resembles both the physiochemical and the biological properties of the analyte. Despite the fact that retrodialysis by drug cannot be used for endogenous compounds as it requires absence of analyte from the sampling site, this calibration method is most commonly used for exogenous compounds in clinical settings.
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The characteristic smear pattern produced by the slow release of the analyte from the complex during the experiment can be used to calculate the dissociation constant of the complex. Dynamic equilibrium ACE involves the combination of the analyte found in the sample and its receptor molecule found in the buffered solution in the capillary tube so that binding and separation only occur in the instrument. It is assumed for dynamic equilibrium affinity capillary electrophoresis that ligand-receptor binding occurs rapidly when the analyte and buffer are mixed. Binding constants are generally derived from this technique based upon the peak migration shift of the receptor which is dependent upon the concentration of the analyte in the sample.
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Chemical ionization was developed in the 1960s. Ionization of sample (analyte) is achieved by interaction of its molecules with reagent ions. The analyte is ionized by ion-molecule reactions during collisions in the source. The process may involve transfer of an electron, a proton or other charged species between the reactants.
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To make a potentiometric determination of an analyte in a solution, the potential of the cell is measured. This measurement must be corrected for the reference and junction potentials. It can also be used in standardisation methods. The concentration of the analyte can then be calculated from the Nernst Equation.
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The technique makes use of the atomic absorption spectrum of a sample in order to assess the concentration of specific analytes within it. It requires standards with known analyte content to establish the relation between the measured absorbance and the analyte concentration and relies therefore on the Beer-Lambert law.
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It must not react with either the analyte or the supporting electrolyte. It must be pure to prevent interference.
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An assay is an investigative (analytic) procedure in laboratory medicine, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a target entity (the analyte). The analyte can be a drug, biochemical substance, or cell in an organism or organic sample. The measured entity is often called the analyte, the measurand, or the target of the assay. An assay usually aims to measure an analyte's intensive property and express it in the relevant measurement unit (e.g.
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A reagentless biosensor can monitor a target analyte in a complex biological mixture without additional reagent. Therefore, it can function continuously if immobilized on a solid support. A fluorescent biosensor reacts to the interaction with its target analyte by a change of its fluorescence properties. A Reagentless Fluorescent biosensor (RF biosensor) can be obtained by integrating a biological receptor, which is directed against the target analyte, and a solvatochromic fluorophore, whose emission properties are sensitive to the nature of its local environment, in a single macromolecule.
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The determination of enantiomeric purity and absolute configuration is frequently necessary in organic synthesis. Pirkle's alcohol is applied to obtain this information by NMR spectroscopy. When Pirkle's alcohol is in solution with an ensemble of chiral molecules, short- lived diastereomeric solvates may be formed from Pirkle's alcohol and the enantiomers of the analyte. Enantiomorphic protons of the analyte enantiomers, which without Pirkle's alcohol are indistinguishable by NMR, become diastereomorphic when the analyte interacts with Pirkle's alcohol, and appear as different signals in an NMR spectrum.
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The solubility of an analyte can change drastically with its overall charge; as such it is common for reduced or oxidized analyte species to precipitate out onto the electrode. This layering of analyte can insulate the electrode surface, display its own redox activity in subsequent scans, or otherwise alter the electrode surface in a way that affects the CV measurements. For this reason it is often necessary to clean the electrodes between scans. Common materials for the working electrode include glassy carbon, platinum, and gold.
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A solution containing the analyte, A, in the presence of some conductive buffer. If an electrolytic potential is applied to the solution through a working electrode, then the measured current depends (in part) on the concentration of the analyte. Measurement of this current can be used to determine the concentration of the analyte directly; this is a form of amperometry. However, the difficulty is that the measured current depends on several other variables, and it is not always possible to control all of them adequately.
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Written as a reduction, cathodic current is positive. The net current density is the difference between the cathodic and anodic current density. Exchange current densities reflect intrinsic rates of electron transfer between an analyte and the electrode. Such rates provide insights into the structure and bonding in the analyte and the electrode.
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Sometimes an internal standard is added at a known concentration directly to an analytical sample to aid in quantitation. The amount of analyte present is then determined relative to the internal standard as a calibrant. An ideal internal standard is isotopically-enriched analyte which gives rise to the method of isotope dilution.
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The main desorption mechanism in DAPPI is thermal desorption due to rapid heating of the surface. Therefore, DAPPI only works well for surfaces of low thermal conductivity. The ionization mechanism depends on the analyte and solvent used. For example, the following analyte (M) ions may be formed: [M + H]+, [M - H]−, M+•, M−•.
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This allows selective ionization of an analyte from a mixture of compounds, where accurate and precised results can be obtained.
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Electrochemical biosensors contain a biorecognition element that selectively reacts with the target analyte and produces an electrical signal that is proportional to the analyte concentration. In general, there are several approaches that can be used to detect electrochemical changes during a biorecognition event and these can be classified as follows: amperometric, potentiometric, impedance, and conductometric.
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The amount of labeled antibody on the site is then measured. It will be directly proportional to the concentration of the analyte because labeled antibody will not bind if the analyte is not present in the unknown sample. This type is also known as sandwich assay as the analyte is "sandwiched" between two antibodies.) Heterophile antibodies may thus give false positives (by bridging the capture and signal antibody) or false negatives (by blocking one or the other). Both detecting and deterring this interference is difficult in clinical medicine.
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Schematic of matrix-assisted inlet ionization (MAII) In Matrix- assisted inlet ionization (MAII), a matrix which can be a solvent is used at ambient temperature with the analyte of interest as a mixture. The matrix/analyte mixture is inserted into the heated inlet tube through tapping the mixture at the opening end of the tube. For the highly charged ions of the analyte to be produced from ionization, desolvation of the matrix molecules needs to occur. Matrices that can be used include: 2,5-dihydroxybenzoic acid, 2,5-dihydroxyacetophenone, 2-aminobenzyl alcohol, anthranilic acid, and 2-hydroxyacetophenone.
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The kinase phosphorylates the 5'-end of the analyte and the ligase will join the capture probe to the analyte to the detection probe. The capture and detection probes in the DLA can thus be termed ligation probes. As for the hybridization-ligation assay, the DLA is specific for the parent compound because the efficiency of ligation over a bulge loop is low, and thus the DLA detects the full-length analyte with both intact 5' and 3'-ends. The DLA can also be used for the determination of individual metabolites in biological matrices.
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The third proposed theory for ion suppression in ESI relates to the presence of non-volatile species which can either cause co-precipitation of analyte in the droplet (thus preventing ionisation) or prevent the contraction of droplet size to the critical radius required for the ion evaporation and/or charge residue mechanisms to form gas phase ions efficiently. It is worthwhile to consider that the degree of ion suppression may be dependent on the concentration of the analyte being monitored. A higher analyte/matrix ratio can give a reduced effect of ion suppression.
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Matrix-Assisted Ionization [MAI] is similar to MALDI in sample preparation, but a laser is not required to convert analyte molecules included in a matrix compound into gas- phase ions. In MAI, analyte ions have charge states similar to electrospray ionization but obtained from a solid matrix rather than a solvent. No voltage or laser is required, but a laser can be used to obtain spatial resolution for imaging. Matrix-analyte samples are ionized in the vacuum of a mass spectrometer and can be inserted into the vacuum through an atmospheric pressure inlet.
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Ion-attachment mass spectrometry (IAMS) is a form of mass spectrometry that uses a "soft" form of ionization similar to chemical ionization in which a cation is attached to the analyte molecule in a reactive collision: :{M} + {X+} + A -> {MX+} + A Where M is the analyte molecule, X+ is the cation and A is a non-reacting collision partner.
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Liquid-liquid extractions can be carried out on digital microfluidic device by taking advantage of immiscible liquids.9 Two droplets, one containing the analyte in aqueous phase, and the other an immiscible ionic liquid are present on the electrode array. The two droplets are mixed and the ionic liquid extracts the analyte, and the droplets are easily separable.
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The build-up of analyte over time allows to quantify on rates (kon), off rates (koff), dissociation constants (Kd) and, in some applications, active concentrations of the analyte. Several different vendors offer SPR-based devices. Best known are Biacore instruments which were the first commercially available. Dual polarisation interferometry (DPI) can be used to measure protein–protein interactions.
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The advantage of using cantilever sensors is that there is no need for an optically detectable label on the analyte or bioreceptors.
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Various organic solvents may be used to replace water since they compete less effectively with the analyte for proton donation or acceptance.
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Dual Ligation Hybridization AssayThe dual ligation hybridization assay (DLA) extends the specificity of the hybridization-ligation assay to a specific method for the parent compound. Despite hybridization-ligation assay's robustness, sensitivity and added specificity for the 3'-end of the oligonculeotide analyte, the hybridization-ligation assay is not specific for the 5' end of the analyte. The DLA is intended to quantify the full-length, parent oligonucleotide compound only, with both intact 5' and 3' ends. DLA probes are ligated at the 5' and 3' ends of the analyte by the joint action of T4 DNA ligase and T4 polynucleotide kinase.
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Adding known quantities of analyte(s) of interest is a distinct technique called standard addition, which is performed to correct for matrix effects. This ratio for the samples is then used to obtain their analyte concentrations from a calibration curve. The internal standard used needs to provide a signal that is similar to the analyte signal in most ways but sufficiently different so that the two signals are readily distinguishable by the instrument. For example, deuterated chlorobenzene (C6D5Cl) is an internal standard used in the analysis of volatiles on GC-MS because it is similar to Chlorobenzene but does not occur naturally.
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Other parameters that can be used to alter the order or time of retention are the carrier gas flow rate, column length and the temperature.Diagram of a gas chromatograph.In a GC analysis, a known volume of gaseous or liquid analyte is injected into the "entrance" (head) of the column, usually using a microsyringe (or, solid phase microextraction fibers, or a gas source switching system). As the carrier gas sweeps the analyte molecules through the column, this motion is inhibited by the adsorption of the analyte molecules either onto the column walls or onto packing materials in the column.
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The stable isotope is almost guaranteed to be chemically and physically as close as possible to the analyte of interest, hence producing an almost identical detector response in addition to behaving identically during sample preparation and chromatographic resolution. To this end, the ion suppression experienced by both the analyte and the internal standard should be identical. It is important to note that an excessively high concentration of stable isotope internal standard may cause ion suppression itself, since it will co- elute with the analyte of interest. Hence, the internal standard should be added at an appropriate concentration.
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During calibration with the no-net-flux-method, the microdialysis probe is perfused with at least four different concentrations of the analyte of interest (Cin) and steady-state concentrations of the analyte leaving the probe are measured in the dialysate (Cout). The recovery for this method can be determined by plotting Cout−Cin over Cin and computing the slope of the regression line. If analyte concentrations in the perfusate are equal to concentrations at the sampling site, no-net flux occurs. Respective concentrations at the no-net-flux point are represented by the x-intercept of the regression line.
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A ChemFET's source and drain are constructed as for an ISFET, with the gate electrode separated from the source electrode by a solution. The gate electrode's interface with the solution is a semi-permeable membrane containing the receptors, and a gap to allow the substance under test to come in contact with the sensitive receptor moieties. A ChemFET's threshold voltage depends on the concentration gradient between the analyte in solution and the analyte in contact with its receptor-embedded semi-permeable barrier. Often, ionophores are used to facilitate analyte ion mobility through the substrate to the receptor.
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Using matrix matched calibration standards can compensate for ion suppression. Using this technique, calibration standards are prepared in identical sample matrix to that used for analysis (e.g. plasma) by spiking a normal sample with known concentrations of analyte. This is not always possible for biological samples, since the analyte of interest is often endogenously present in a clinically significant, albeit normal, quantity.
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A CI experiment involves the use of gas phase acid-base reactions in the chamber. Ions are produced through the collision of the analyte with ions of a reagent gas that are present in the ion source. Some common reagent gases include: methane, ammonia, water and isobutane. Inside the ion source, the reagent gas is present in large excess compared to the analyte.
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However, it should also be considered that the analyte of interest may not be ionised effectively in negative mode either, rendering this approach useless.
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This mechanism shows the solvent (S) and the analyte (M) in desorption atmospheric pressure photoionization going through both positive ion and negative ion reaction.
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This concentration gradient of charged analyte ions creates a chemical potential between the source and gate, which is in turn measured by the FET.
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Thus, the signal measured by XPS is an exponentially surface-weighted signal, and this fact can be used to estimate analyte depths in layered materials.
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Typically, a conventional three-electrode system is made specific to the analyte by immobilizing a biorecognition element to the surface. A voltage is applied and the current is measured. The interfacial impedance between the electrode and solution changes as a result of the analyte binding. An impedance analyzer can be used to control and apply the stimulus as well as measure the impedance changes.
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Another drawback is the possibility of interaction between the stationary phase and the analyte. Any interaction leads to a later elution time and thus mimics a smaller analyte size. When performing this method, the bands of the eluting molecules may be broadened. This can occur by turbulence caused by the flow of the mobile phase molecules passing through the molecules of the stationary phase.
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Traditionally, chemical sensing has been approached with a system that contains a covalently bound indicator to a receptor though a linker. Once the analyte binds, the indicator changes color or fluoresces. This technique is called the indicator-spacer-receptor approach (ISR). In contrast to ISR, Indicator-Displacement Assay (IDA) utilizes a non-covalent interaction between a receptor (the host), indicator, and an analyte (the guest).
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The sorbent tube and the focusing trap may be packed with one or more sorbents. The type and number of sorbents depends on a number of factors including the sampling setup, the analyte volatility range, analyte concentration, and the humidity of the sample. One of the most versatile and popular sorbents for thermal desorption is poly(2,6-diphenyl-p-phenylene oxide), known by its trademark Tenax.
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Powdered bis(dimethylglyoximate)nickel. This coordination compound can be used for the gravimetric determination of nickel. The term “equivalent weight” had a distinct sense in gravimetric analysis: it was the mass of precipitate which corresponds to one gram of analyte (the species of interest). The different definitions came from the practice of quoting gravimetric results as mass fractions of the analyte, often expressed as a percentage.
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This technique requires the transfer of high-mass entities from the reagent gas to the analyte, and therefore, the Franck-Condon principle does not govern the process of ionization. CI is thus quite useful in cases where the energy of the bombarding electrons in EI is high, resulting exclusively in fragmentation of the analyte, causing the molecular-ion peak to be less detectable or completely absent.
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The matrix should not compete with the analyte molecule, so the matrix should not want to form the same type of ion as the analyte. For example, if the desired analyte has a high amount of acidity, it would be logical to choose a matrix with a high amount of basicity to avoid competition and facilitate the formation of an ion. The pH of the matrix can also be used to select what sample you want to obtain spectra for. For example, in the case of proteins, a very acidic pH can show very little of the peptide components, but can show very good signal for those components that are larger.
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In off-line measurements, the analyte solution is applied directly to the mass spectrometer by a spray capillary . Off-line sample preparation has many considerations, such as the fact that the capillary used allows for the application of volumes in the nanoliter range, which can contain a concentration too small for analysis of many compounds, such as proteins. An additional problem can be loss of ESI signal due to interference between the analyte sample and background components. Unfortunately, it has been shown that sample preparation itself can only slightly alleviate this problem which is due more to the nature of the analyte itself than the preparation.
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It has been largely superseded by other techniques such as atomic absorption spectroscopy, in which the mass of analyte is read off from a calibration curve.
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The mechanism for the instrument's response to the analyte may be predicted or understood according to some theoretical model, but most such models have limited value for real samples. (Instrumental response is usually highly dependent on the condition of the analyte, solvents used and impurities it may contain; it could also be affected by external factors such as pressure and temperature.) Many theoretical relationships, such as fluorescence, require the determination of an instrumental constant anyway, by analysis of one or more reference standards; a calibration curve is a convenient extension of this approach. The calibration curve for a particular analyte in a particular (type of) sample provides the empirical relationship needed for those particular measurements. The chief disadvantages are (1) that the standards require a supply of the analyte material, preferably of high purity and in known concentration, and (2) that the standards and the unknown are in the same matrix.
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Polyatomic ions generated within the plasma can have larger atomic radii than analyte ions of similar mass, i.e. the interferent NaAr+ (mass 63) is larger than the analyte Cu+ (mass 63). Thus, when using a collisional/reactive gas mixture, these larger species undergo more collisions/reactions in the cell, in which they lose increasingly more energy, and are then excluded from the quadrupole mass filter by the kinetic energy barrier.
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Chemosensors are nano-sized molecules and for application in vivo need to be non-toxic. A chemosensor must be able to give a measurable signal in direct response to the analyte recognition. Hence, the signal response is directly related to the magnitude of the sensing event (and, in turn concentration of the analyte). While the signalling moiety acts as a signal transducer, converting the recognition event into an optical response.
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The FIDA principle: A narrow indicator zone is introduced into a capillary under hydrodynamic flow. When the indicator is not bound, a narrow peak is observed at the detector. However, when the indicator is bound by the target analyte, the apparent size increases and a broader peak is observed. This change in size can be used for determine the analyte concentration and interaction \- Published by The Royal Society of Chemistry.
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In thermal ionization mass spectrometry, small quantities of highly purified analyte are deposited onto a clean metal filament. Rhenium or tungsten are typically used. The sample is heated in a vacuum of the ion source by applying a current to the filaments. A portion of the analyte will be ionized by the filament and then are directed down the flight tube and separated based on mass to charge ratios.
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As a result of the presence and biochemical action of the analyte (target of interest), a physico-chemical change is produced within the biorecognition layer that is measured by the physicochemical transducer producing a signal that is proportionate to the concentration of the analyte. The physicochemical transducer may be electrochemical, optical, electronic, gravimetric, pyroelectric or piezoelectric. Based on the type of biotransducer, biosensors can be classified as shown to the right.
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This means that, in a particulate column, a given analyte may diffuse into and out of the same pore, or enter through one pore and exit through a connected pore. By contrast, an analyte in a monolith is able to enter one channel and exit through any of 6 or more different venues.“Eliminating the downstream processing bottleneck with monoliths and simulated moving bed chromatography.” Pete Gagnon, BioProcess International, September 2008.
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Protein Microarrays-Based Strategies for Life Detection in Astrobiology. Víctor Parro, Luis A. Rivas, and Javier Gómez-Elvira. Space Science Reviews, March 2008, Volume 135, Issue 1–4, pp 293–311. The technique called "sandwich immunoassay" is a non-competitive immunoassay in which the analyte (compound of interest in the unknown sample) is captured by an immobilized antibody, then a labeled antibody is bound to the analyte to reveal its presence.
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The electrodes are immobile and sit in unstirred solutions during cyclic voltammetry. This "still" solution method gives rise to cyclic voltammetry's characteristic diffusion-controlled peaks. This method also allows a portion of the analyte to remain after reduction or oxidation so that it may display further redox activity. Stirring the solution between cyclic voltammetry traces is important in order to supply the electrode surface with fresh analyte for each new experiment.
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Since the analyte and bio-receptor now bind to the gold, it increases the apparent mass of the analyte and therefore amplified the signal. These properties had been used to build DNA sensor with 1000-fold sensitive than without the Au NP. Humidity senor was also built by altering the atom interspacing between molecules with humidity change, the interspacing change would also result in a change of the Au NP's LSPR.
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Analyte-specific reagents (ASRs) are a class of biological molecules which can be used to identify and measure the amount of an individual chemical substance in biological specimens.
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The sample spray in EESI produces a liquid aerosol with the analyte in sample droplets.Law, W.S., et al., On the Mechanism of Extractive Electrospray Ionization. Analytical Chemistry, 2010.
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The situation may be more complex for lipophilic compounds as they can stick to the tubing or other probe components, resulting in a low or no analyte recovery.
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Stringent, low/no salt wash will remove un-ligated products. The ligation of the analyte to the ligation probe makes the method specific for the 3'-end of the analyte, ligation by T4 DNA ligase being much less efficient over a bulge loop, which would happen for a 3' metabolite N-1 version of the analyte, for example. The specificity of the hybridization-ligation assay for ligation at the 3'-end is particularly relevant because the predominant nucleases in blood are 3' to 5' exonucleases. One limitation of the method is that it requires a free 3'-end hydroxyl which may not be available when targeting moieties are attached to the 3'-end, for example.
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In such situations there is concern that the analyte and trace redox products may interact with the reference electrode and either render it useless or increase drift. As a result, even these simple references are commonly sequestered in their own cells. The more complex references such as standard hydrogen electrode, saturated calomel electrode, or silver chloride electrode(specific concentration) can not directly mix the analyte solution for fear the electrode will fall apart or interact/react with the analyte. A bulk electrolysis is best performed in a three part cell in which both the auxiliary electrode and reference electrode have their own cell which connects to the cell containing the working electrode.
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Magneto-electrochemical assays are based on the use of magnetic nanoparticles in electrochemical sensing either by being distributed through a sample where they can collect and preconcentrate the analyte and handled by a magnetic field or by modifying an electrode surface enhancing its conductivity and the affinity with the analyte. Coated-magnetic nanoparticles have a key aspect in electrochemical sensing not only because it facilitates the collecting of analyte but also it allows MNPs to be part of the sensor transduction mechanism. For the manipulation of MNPs in electrochemical sensing has been used magnetic electrode shafts or disposable screen-printed electrodes integrating permanent bonded magnets, aiming to replace magnetic supports or any external magnetic field.
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Reversed phase SPE separates analytes based on their polarity. The stationary phase of a reversed phase SPE cartridge is derivatized with hydrocarbon chains, which retain compounds of mid to low polarity due to the hydrophobic effect. The analyte can be eluted by washing the cartridge with a non-polar solvent, which disrupts the interaction of the analyte and the stationary phase. A stationary phase of silicon with carbon chains is commonly used.
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An analyte, component (in clinical chemistry), or chemical species is a substance or chemical constituent that is of interest in an analytical procedure. The purest substances are referred to as analytes. Example : 24 karat gold, NaCl, water, etc. In reality, no substance has been found to be 100% pure in its quality, so we call a substance that is found to be most pure (for some metals, 99% after electrolysis) an analyte.
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The matrix is then thought to transfer protons to the analyte molecules (e.g., protein molecules), thus charging the analyte. An ion observed after this process will consist of the initial neutral molecule [M] with ions added or removed. This is called a quasimolecular ion, for example [M+H]+ in the case of an added proton, [M+Na]+ in the case of an added sodium ion, or [M-H]− in the case of a removed proton.
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This model also suggests that metal ion adducts (e.g., [M+Na]+ or [M+K]+) are mainly generated from the thermally induced dissolution of salt. The matrix-assisted ionization (MAI) method uses matrix preparation similar to MALDI but does not require laser ablation to produce analyte ions of volatile or nonvolatile compounds. Simply exposing the matrix with analyte to the vacuum of the mass spectrometer creates ions with nearly identical charge states to electrospray ionization.
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Tetralin eluted at approximately 35 minutes using the GC-MS method conditions, whereas the analyte had a retention time of less than 7 minutes when the GC-VUV method was applied. The co-elution of m- and p-xylene occurred in both GC-MS and GC-VUV method runs. VUV software matched the analyte absorbance of both isomers with VUV library spectra (Figure 2) to deconvolve the overlapping signals as displayed in Figure 6.
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Flow-induced dispersion analysis (FIDA), is a new capillary-based and immobilization-free technology used for characterization and quantification of biomolecular interaction and protein concentration under native conditions. The technique is based on measuring the change in apparent size (hydrodynamic radius) of a selective ligand when interacting with the analyte of interest. A FIDA assay works in complex solutions (e.g. plasma ), and provides information regarding analyte concentration, affinity constants, molecular size and binding kinetics.
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Relevant to cyclic voltammetry, the diffusion layer has negligible volume compared the volume of the bulk solution. For this reason, cyclic voltammetry experiments have an inexhaustible supply of fresh analyte.
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The use of deuterium HCL is preferable compared to an arc lamp due to the better fit of the image of the former lamp with that of the analyte HCL.
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The eluate is the analyte material that emerges from the chromatograph. It specifically includes both the analytes and solutes passing through the column, while the eluent is only the carrier.
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This is often an isotopically labeled version of the analyte. There are forms of mass spectrometry, such as accelerator mass spectrometry that are designed from the bottom up to be quantitative.
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This paper shows the theoretical and practical difficulties, which have to be considered and solved when real samples need to be analysed in a wide range of analyte and interferant concentrations.
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Cation exchange sorbents are derivatized with functional groups that interact and retain positively charged cations, such as bases. Strong cation exchange sorbents contain aliphatic sulfonic acid groups that are always negatively charged in aqueous solution, and weak cation exchange sorbents contain aliphatic carboxylic acids, which are charged when the pH is above about 5. Strong cation exchange sorbents are useful because any strongly basic impurities in the sample will bind to the sorbent and usually will not be eluted with the analyte of interest; to recover a strong base a weak cation exchange cartridge should be used. To elute the analyte from either the strong or weak sorbent, the stationary phase is washed with a solvent that neutralizes ionic interaction between the analyte and the stationary phase.
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Flow- through tests typically come in the form of cassettes divided into four parts: an upper casing, a reactive membrane panel, an absorbent panel, and a lower casing. To perform a test, a diluted sample is applied to the reactive membrane panel and flows through to the absorbent pad, with the target analyte being captured in the membrane. The membrane is then washed to remove unbound, non-target molecules, washed again with a solution containing a signal reagent, and washed again to remove unbound signal reagent. If the analyte was present in the original sample, then by the end of this process it should be bound to the membrane, with the signal reagent bound to it, revealing (usually visually) the presence of the analyte on the membrane.
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Ion suppression in LC-MS and LC-MS/MS refers to reduced detector response, or signal:noise as a manifested effect of competition for ionisation efficiency in the ionisation source, between the analyte(s) of interest and other endogenous or exogenous (e.g. plasticisers extracted from plastic tubes, mobile phase additives) species which have not been removed from the sample matrix during sample preparation. Ion suppression is not strictly a problem unless interfering compounds elute at the same time as the analyte of interest. In cases where ion suppressing species do co-elute with an analyte, the effects on the important analytical parameters including precision, accuracy and limit of detection (analytical sensitivity) can be extensive, severely limiting the validity of an assay's results.
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Analysis of soil samples by titration. A typical titration begins with a beaker or Erlenmeyer flask containing a very precise amount of the analyte and a small amount of indicator (such as phenolphthalein) placed underneath a calibrated burette or chemistry pipetting syringe containing the titrant. Small volumes of the titrant are then added to the analyte and indicator until the indicator changes color in reaction to the titrant saturation threshold, representing arrival at the endpoint of the titration, meaning the amount of titrant balances the amount of analyte present, according to the reaction between the two. Depending on the endpoint desired, single drops or less than a single drop of the titrant can make the difference between a permanent and temporary change in the indicator.
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In countercurrent chromatography centrifugal or gravitational forces immobilize the stationary liquid layer. By eliminating solid supports, permanent adsorption of the analyte onto the column is avoided, and a high recovery of the analyte can be achieved. The countercurrent chromatography instrument is easily switched between normal phase chromatography and reversed-phase chromatography simply by changing the mobile and stationary phases. With column chromatography, the separation potential is limited by the commercially available stationary phase media and its particular characteristics.
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Photopolymerization-based signal amplification (PBA) is a method of amplifying detection signals from molecular recognition events in an immunoassay by utilizing a radical polymerization initiated through illumination by light. To contrast between a negative and a positive result, PBA is linked to a colorimetric method, thereby resulting in a change in color when a targeted analyte is detected, i.e., a positive signal. PBA is also used to quantify the concentration of the analyte by measuring intensity of the color.
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The data - the concentrations of the analyte and the instrument response for each standard - can be fit to a straight line, using linear regression analysis. This yields a model described by the equation y = mx + y0, where y is the instrument response, m represents the sensitivity, and y0 is a constant that describes the background. The analyte concentration (x) of unknown samples may be calculated from this equation. Many different variables can be used as the analytical signal.
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Ion- attachment ionization is similar to chemical ionization in which a cation is attached to the analyte molecule in a reactive collision: :M + X+ + A -> MX+ + A Where M is the analyte molecule, X+ is the cation and A is a non-reacting collision partner. In a radioactive ion source, a small piece of radioactive material, for instance 63Ni or 241Am, is used to ionize a gas. This is used in ionization smoke detectors and ion mobility spectrometers.
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The general use and design of CDAs obey the following rules so that the CDA can effectively determine the stereochemistry of an analyte: # The CDA must be enatiomerically pure, or (less satisfactorily) its enantiomeric purity must be accurately known. #The reaction of the CDA with both enantiomers should go to completion under reaction conditions. This acts to avoid enrichment or depletion of one enantiomer of the analyte by kinetic resolution. # CDA must not racemize under derivatization or analysis conditions.
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Basic principle of isotope dilution Adding of an isotopically altered standard to the sample changes the natural isotopic composition of the analyte. By measuring the resulting isotopic composition, it is possible to calculate the amount of the analyte present in the sample. Isotope dilution analysis is a method of determining the quantity of chemical substances. In its most simple conception, the method of isotope dilution comprises the addition of known amounts of isotopically-enriched substance to the analyzed sample.
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Gas phase titration has several advantages over simple spectrophotometry. First, the measurement does not depend on path length, because the same path length is used for the measurement of both the excess titrant and the product. Second, the measurement does not depend on a linear change in absorbance as a function of analyte concentration as defined by the Beer-Lambert law. Third, it is useful for samples containing species which interfere at wavelengths typically used for the analyte.
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The stationary phases are usually finely ground powders or gels and/or are microporous for an increased surface, though in EBA a fluidized bed is used. There is an important ratio between the stationary phase weight and the dry weight of the analyte mixture that can be applied onto the column. For silica column chromatography, this ratio lies within 20:1 to 100:1, depending on how close to each other the analyte components are being eluted.
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The internal standard selected should be again similar to the analyte and have a similar retention time and similar derivitization. It must be stable and must not interfere with the sample components.
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The experiment itself involves having a radioactive positron source (often 22Na) situated near the analyte. Positrons are emitted near-simultaneously with gamma rays. These gamma rays are detected by a nearby scintillator.
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In contrast, when the redox analyte is in solution and diffuses to/from the electrode, the peak current is proportional to the square root of the scan rate (see: Randles–Sevcik equation).
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Surface- enhanced laser desorption/ionization (SELDI) is a variant of MALDI that is used for the analysis of protein mixtures that uses a target modified to achieve biochemical affinity with the analyte compound.
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True moving bed chromatography (TMBC) is only a theoretical concept. Its simulation, SMBC is achieved by the use of a multiplicity of columns in series and a complex valve arrangement, which provides for sample and solvent feed, and also analyte and waste takeoff at appropriate locations of any column, whereby it allows switching at regular intervals the sample entry in one direction, the solvent entry in the opposite direction, whilst changing the analyte and waste takeoff positions appropriately as well.
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Flowing-afterglow mass spectrometry uses a flowing afterglow to create protonated water cluster ions in a helium or argon carrier gas in a flow tube that react with sample molecules that are measured by a mass spectrometer downstream. These systems can be used for trace gas analysis. This works by keeping the initial ionization source spatially separated from the target analyte and channeling the afterglow of the initial ionization towards the analyte. Analytes are added downstream to create ion products.
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There are two main assaying techniques: heterogeneous and homogeneous. If two lanthanide chelates are used in the analysis one after the other—it is called heterogeneous assaying. The first analyte is linked to a specific binding agent on a solid support such as a polymer and then another reaction couples the first poorly luminescent lanthanide complex with a new better one. This tedious method is used because the second more luminescent compound would not bind without the first analyte already present.
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Fragmentation can be rarely observed for some molecules. 280px Use of DART compared to traditional methods minimizes sample amount, sample preparation, eliminates extraction steps, decreases limit of detection and analysis time. Also it provides a broad range sensitivity, simultaneous determination of multi-drug analytes and sufficient mass accuracy for formulation determination. The DART ion source is a kind of gas-phase ionization, and it requires some sort of volatility of the analyte to support thermally assisted desorption of analyte ions.
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Proteins or antibodies acting as probe molecules can then covalently bind to the disk surface and can be incubated. A polydimethylsiloxane (PDMS) channel plate can also be used to immobilize the probes in a line array. The plate is removed, and the process is repeated with another plate to deliver analyte samples in a line array perpendicular to the probe array. The probe and analyte samples can bind or hybridize at the intersections of the arrays to create rectangular hybridization sites.
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In this approach, the sample is spiked with a species (internal standard) which is used to normalise the response of analyte, compensating for variables at any stage of the sample preparation and analysis, including ion suppression. It is important that the internal standard displays very similar (ideally identical) properties, with respect to detector response (i.e. ionisation), as the analyte of interest. To simplify the selection of internal standard, most laboratories use an analogous stable isotope in an isotope dilution type analysis.
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The U.S. Food and Drug Administration (FDA) defines analyte specific reagents (ASRs) in 21 CFR 864.4020 as “antibodies, both polyclonal and monoclonal, specific receptor proteins, ligands, nucleic acid sequences, and similar reagents which, through specific binding or chemical reaction with substances in a specimen, are intended to use in a diagnostic application for identification and quantification of an individual chemical substance or ligand in biological specimens.” In simple terms an analyte specific reagent is the active ingredient of an in-house test.
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However, given that the general principles in these assays are largely similar, they are often grouped in the same category as ELISAs. In 2012, an ultrasensitive, enzyme-based ELISA test using nanoparticles as a chromogenic reporter was able to give a naked- eye colour signal, from the detection of mere attograms of analyte. A blue color appears for positive results and red color for negative. Note that this detection only can confirm the presence or the absence of analyte, not the actual concentration.
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Atmospheric pressure photoionization uses a source of photons, usually a vacuum UV (VUV) lamp, to ionize the analyte with single photon ionization process. Analogous to other atmospheric pressure ion sources, a spray of solvent is heated to relatively high temperatures (above 400 degrees Celsius) and sprayed with high flow rates of nitrogen for desolvation. The resulting aerosol is subjected to UV radiation to create ions. Atmospheric pressure laser ionization uses UV laser light sources to ionize the analyte via MPI.
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The two most common gravimetric methods using volatilization are those for water and carbon dioxide. An example of this method is the isolation of sodium hydrogen bicarbonate (the main ingredient in most antacid tablets) from a mixture of carbonate and bicarbonate. The total amount of this analyte, in whatever form, is obtained by addition of an excess of dilute sulfuric acid to the analyte in solution. In this reaction, nitrogen gas is introduced through a tube into the flask which contains the solution.
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VUV absorption is additive, meaning that overlapping peaks give a spectrum that corresponds to the sum absorbance of each compound. The individual contribution of each analyte can be determined if the VUV spectra for co-eluting compounds are stored in the VUV library.K.A. Schug, I.C. Santos. Recent advances and applications of gas chromatography vacuum ultraviolet spectroscopy, J. Sep. Sci. 2017, 40, 138–151 The ability to differentiate coeluting analyte spectra and use them to deconvolve the overlapping signals is demonstrated in Figure 4.
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Mass spectrometry is not inherently quantitative because of differences in the ionization efficiency and/or detectability of the many peptides in a given sample, which has sparked the development of methods to determine relative and absolute abundance of proteins in samples. The intensity of a peak in a mass spectrum is not a good indicator of the amount of the analyte in the sample, although differences in peak intensity of the same analyte between multiple samples accurately reflect relative differences in its abundance.
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A burette and Erlenmeyer flask (conical flask) being used for an acid–base titration. Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the titrant or titrator, is prepared as a standard solution of known concentration and volume. The titrant reacts with a solution of analyte (which may also be termed the titrand) to determine the analyte's concentration.
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Anion exchange sorbents are derivatized with positively charged functional groups that interact and retain negatively charged anions, such as acids. Strong anion exchange sorbents contain quaternary ammonium groups that have a permanent positive charge in aqueous solutions, and weak anion exchange sorbents use amine groups which are charged when the pH is below about 9. Strong anion exchange sorbents are useful because any strongly acidic impurities in the sample will bind to the sorbent and usually will not be eluted with the analyte of interest; to recover a strong acid a weak anion exchange cartridge should be used. To elute the analyte from either the strong or weak sorbent, the stationary phase is washed with a solvent that neutralizes the charge of either the analyte, the stationary phase, or both.
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An internal standard in analytical chemistry is a chemical substance that is added in a constant amount to samples, the blank and calibration standards in a chemical analysis. This substance can then be used for calibration by plotting the ratio of the analyte signal to the internal standard signal as a function of the analyte concentration of the standards. This is done to correct for the loss of analyte during sample preparation or sample inlet. The internal standard is a compound that is very similar, but not identical to the chemical species of interest in the samples, as the effects of sample preparation should, relative to the amount of each species, be the same for the signal from the internal standard as for the signal(s) from the species of interest in the ideal case.
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Threads are also relatively strong and difficult to break from handling which makes them stable over time and easy to transport. Thread-based microfluidics has been applied to 3D tissue engineering and analyte analysis.
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After extraction, the SPME fiber is transferred to the injection port of separating instruments, such as a gas chromatography and mass spectrometry, where desorption of the analyte takes place and analysis is carried out.
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Silver metal is more easily detectable by cameras, scanners, or other drives than is the analyte alone. Still, this enhancement procedure requires many additional reaction and washing steps which could lead to analytical errors.
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In most EQA schemes, laboratories receive scores for their results. The most popular score is the Z-score, also called standard deviation index (SDI). The score is given per analyte and per test item.
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One in particular, due to increasing studies into optimization of DESI is, Nanospray desorption electrospray ionization. In this technique the analyte is desorbed into a bridge formed via two capillaries and the analysis surface.
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The Karl Fischer titration for water content is another nonaqueous titration, usually done in methanol or sometimes in ethanol. Since water is the analyte in this method, it cannot also be used as the solvent.
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A molecular sensor is a molecule that interacts with an analyte to produce a detectable change. Molecular sensors combine molecular recognition with some form of reporter, so the presence of the item can be observed.
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The needle is then raised to be level with the mass spectrometer inlet where a high voltage of 2-3 kV is applied. Electrospray is induced at the tip of the needle, producing analyte ions which are drawn into the mass spectrometer for analysis. The mechanism by which ions are formed is believed to be identical to traditional electrospray ionization. As a result, in positive ion mode analytes are often observed as the protonated, sodiated and potentiated ions, depending on the sample and analyte type.
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This way if the injection volumes (and hence the peak areas) differ slightly, the ratio of the areas of the analyte and the internal standard will remain constant from one run to the next. This comparison of runs also applies to solutions with different concentrations of the analyte. The area of the internal standard becomes the value to which all other areas are referenced. Below is the mathematical derivation and application of this method. Consider an analysis of octane (C8H18) using nonane (C9H20) as the internal standard.
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Standard DVD reader Standard CD/DVD readers can be used to read the assays. The CD/DVD readers contain a laser, set of optical elements which shape and focus the laser, a disk driver, and a signal detector that function as follows: # The laser produces light of a selected wavelength. # The beam of light hits the analyte in the spots of the microarrays and refracts. The mass of the analyte causes the angle of reflected light to be different from the angle of incident light.
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Biosensors used for screening combinatorial DNA libraries In a biosensor, the bioreceptor is designed to interact with the specific analyte of interest to produce an effect measurable by the transducer. High selectivity for the analyte among a matrix of other chemical or biological components is a key requirement of the bioreceptor. While the type of biomolecule used can vary widely, biosensors can be classified according to common types of bioreceptor interactions involving: antibody/antigen, enzymes/ligands, nucleic acids/DNA, cellular structures/cells, or biomimetic materials.
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Sample preparation for mass spectrometry is used for the optimization of a sample for analysis in a mass spectrometer (MS). Each ionization method has certain factors that must be considered for that method to be successful, such as volume, concentration, sample phase, and composition of the analyte solution. Quite possibly the most important consideration in sample preparation is knowing what phase the sample must be in for analysis to be successful. In some cases the analyte itself must be purified before entering the ion source.
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Matrix-assisted laser desorption electrospray ionization (MALDESI) is an atmospheric pressure ionization source for generation of multiply charged ions. An ultraviolet or infrared laser is directed onto a solid or liquid sample containing the analyte of interest and matrix desorbing neutral analyte molecules that are ionized by interaction with electrosprayed solvent droplets generating multiply charged ions. Laser ablation electrospray ionization (LAESI) is an ambient ionization method for mass spectrometry that combines laser ablation from a mid-infrared (mid-IR) laser with a secondary electrospray ionization (ESI) process.
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Laserspray Ionization (LSI) is a newer mass spectrometric technique commonly used with biomolecules, such as proteins. This method is similar to matrix-assisted laser desorption/ionization (MALDI) at atmospheric pressure in that it involves an analyte and matrix mixture. It also contains features from electrospray ionization, in which it produces a similar mass spectra. The mechanism was initially thought to involve laser induced production of highly charge matrix/analyte clusters that upon evaporation of the matrix produces ions by the same mechanism as ESI.
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VUV detectors complement mass spectrometry, which struggles with characterizing constitutional isomers and compounds with low mass quantitation ions. VUV spectra can also be used to deconvolve analyte co- elution, resulting in an accurate quantitative representation of individual analyte contribution to the original response.H. Fan, J. Smuts, L. Bai, P. Walsh, D.W. Armstrong, K.A. Schug, Gas chromatography–vacuum ultraviolet spectroscopy for analysis of fatty acid methyl esters, Food Chem. 2016, 194, 265–271 This characteristically lends itself to significantly reducing GC runtimes through flow rate-enhanced chromatographic compression.
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Back titration is a titration done in reverse; instead of titrating the original sample, a known excess of standard reagent is added to the solution, and the excess is titrated. A back titration is useful if the endpoint of the reverse titration is easier to identify than the endpoint of the normal titration, as with precipitation reactions. Back titrations are also useful if the reaction between the analyte and the titrant is very slow, or when the analyte is in a non-soluble solid.
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ChemFETs can be utilized in either liquid or gas phase to detect target analyte, requiring reversible binding of analyte with a receptor located in the gate electrode membrane. There is a wide range of applications of ChemFETs, including most notably anion or cation selective sensing. More work has been done with cation-sensing ChemFETs than anion- sensing ChemFETs. Anion-sensing is more complicated than cation-sensing in ChemFETs due to many factors, including the size, shape, geometry, polarity, and pH of the species of interest.
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The DME's periodic expansion into the solution and hemispherical shape also affects the way the analyte diffuses to the electrode surface. The DME consists of a fine capillary with a bore size of 20–50 µm.
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Specially coated reflective optics paired with a back-thinned charged coupled device (CCD) enable the collection of high quality VUV absorption data. Figure 1 shows a schematic of the analyte path from GC to VUV detector.
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In 2008, Alpert coined the term, ERLIC (electrostatic repulsion hydrophilic interaction chromatography), for HILIC separations where an ionic column surface chemistry is used to repel a common ionic polar group on an analyte or within a set of analytes, to facilitate separation by the remaining polar groups. Electrostatic effects have an order of magnitude stronger chemical potential than neutral polar effects. This allows one to minimize the influence of a common, ionic group within a set of analyte molecules; or to reduce the degree of retention from these more polar functional groups, even enabling isocratic separations in lieu of a gradient in some situations. His subsequent publication further described orientation effects which others have also called ion-pair normal phase or e-HILIC, reflecting retention mechanisms sensitive to a particular ionic portion of the analyte, either attractive or repulsive.
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Put simply, ion suppression describes the adverse effect on detector response due to reduced ionisation efficiency for analyte(s) of interest, resulting from the presence of species in the sample matrix which compete for ionisation, or inhibit efficient ionisation in other ways. Use of MS/MS as a means of detection may give the impression that there are no interfering species present, since no chromatographic impurities are detected. However, species which are not isobaric may still have an adverse effect on the sensitivity, accuracy and precision of the assay owing to suppression of the ionisation of the analyte of interest. Although the precise chemical and physical factors involved in ion suppression are not fully understood, it has been proposed that basicity, high concentration, mass and more intuitively, co-elution with the analyte of interest are factors which should not be ignored.
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In this case, the analyte molecule could be chemically coupled with a label molecule which is sensitive to APLI. If such a derivatization reaction is available, the selectivity of APLI can be broadened to other molecule classes.
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This produces the species in relatively high amounts. In negative chemical ionization (NCI) the reagent gas decreases the impact of the free electrons on the target analyte. This decreased energy typically leaves the fragment in great supply.
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The analytes are in the vapor phase. This includes breath, odors, VOCs, and other molecules with low volatility that, due to the constant improvements in sensitivity, are detectable in the vapor phase despite of their low vapor pressure. Analyte ions are produced via gas-phase chemical reactions, where charging agents collide with the analyte molecules and transfer their charge. In Secondary Electro-Spray Ionization (SESI), a nano-electrospray operated at high temperature produces nanodroplets that evaporate very rapidly to produce ions and protonated water clusters that ionize the vapors of interest.
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Sandwich hybridization assayIn the sandwich hybridization ELISA assay format, the antigen ligand and antibodies in ELISA are replaced with a nucleic acid analyte, complementary oligonucleotide capture and detection probes. Generally, in the case of nucleic acid hybridization, monovalent salt concentration and temperature are controlled for hybridization and wash stringency, contrary to a traditional ELISA, where the salt concentration will usually be fixed for the binding and wash steps (i.e. PBS or TBS). Thus, optimal salt concentration in hybridization assays varies dependent upon the length and base composition of the analyte, capture and detection probes.
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A. Hierlemann, H. Baltes, "CMOS-based chemical microsensors", The Analyst 128 (1), 2003, pp. 15–28. The recognition component, often called a bioreceptor, uses biomolecules from organisms or receptors modeled after biological systems to interact with the analyte of interest. This interaction is measured by the biotransducer which outputs a measurable signal proportional to the presence of the target analyte in the sample. The general aim of the design of a biosensor is to enable quick, convenient testing at the point of concern or care where the sample was procured.
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Potential against time, current against time and voltammogram (current against potential) for a one-electron, reversible redox couple diffusing freely in solution. The current density is normalised by 0.446 F C sqrt(D F nu / R T). Reductive current counted as negative. Often the analyte displays a reversible CV wave (such as that depicted in Figure 1), which is observed when all of the initial analyte can be recovered after a forward and reverse scan cycle. Although such reversible couples are simpler to analyze, they contain less information than more complex waveforms.
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APLI is a selective ionization method, because the 1+1 REMPI ionization requires an adequate existing electronic intermediate state and both electronic transitions must be quantum mechanically allowed. UV tunability and discrete energy states of analyte allow improved ionization with reduced background signal. In particular polynuclear aromatic compounds fulfil the spectroscopic requirements for 1+1 REMPI, thus APLI is an ideal ionization method for the detection of polycyclic aromatic hydrocarbons (PAH). The selectivity is also a disadvantage, if the direct ionization of an analyte molecule is not possible with APLI.
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In other situations, the matrix, or everything in the solution surrounding the analyte, is the most important factor to consider and adjust. Often, sample preparation itself for mass spectrometry can be avoided by coupling mass spectrometry to a chromatography method, or some other form of separation before entering the mass spectrometer. In some cases, the analyte itself must be adjusted so that analysis is possible, such as in protein mass spectrometry, where usually the protein of interest is cleaved into peptides before analysis, either by in-gel digestion or by proteolysis in solution.
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Atmospheric pressure chemical ionization source Spray ionization methods involve the formation of aerosol particles from a liquid solution and the formation of bare ions after solvent evaporation. Solvent- assisted ionization (SAI) is a method in which charged droplets are produced by introducing a solution containing analyte into a heated inlet tube of an atmospheric pressure ionization mass spectrometer. Just as in Electrospray Ionization (ESI), desolvation of the charged droplets produces multiply charged analyte ions. Volatile and nonvolatile compounds are analyzed by SAI, and high voltage is not required to achieve sensitivity comparable to ESI.
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A chemical sensor is a self-contained analytical device that can provide information about the chemical composition of its environment, that is, a liquid or a gas phase. The information is provided in the form of a measurable physical signal that is correlated with the concentration of a certain chemical species (termed as analyte). Two main steps are involved in the functioning of a chemical sensor, namely, recognition and transduction. In the recognition step, analyte molecules interact selectively with receptor molecules or sites included in the structure of the recognition element of the sensor.
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The extraction efficiency is defined as the ratio between the loss/gain of analyte during its passage through the probe (Cin−Cout) and the difference in concentration between perfusate and distant sampling site (Cin−Csample). In theory, the extraction efficiency of a microdialysis probe can be determined by: 1) changing the drug concentrations while keeping the flow rate constant or 2) changing the flow rate while keeping the respective drug concentrations constant. At steady-state, the same extraction efficiency value is obtained, no matter if the analyte is enriched or depleted in the perfusate.
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Microdialysis probes can consequently be calibrated by either measuring the loss of analyte using drug-containing perfusate or the gain of analyte using drug-containing sample solutions. To date, the most frequently used calibration methods are the low-flow-rate method, the no-net-flux method, the dynamic (extended) no-net-flux method, and the retrodialysis method. The proper selection of an appropriate calibration method is critically important for the success of a microdialysis experiment. Supportive in vitro experiments prior to the use in animals or humans are therefore recommended.
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This method is qualitative, but the addition of mass shifted variants of the analyte for use as an internal standard makes this method useful for quantitative analysis. Pipetor tips, which have been termed MSIA tips or affinity pipette tips play a key role in the process of detecting analytes within biological samples. MSIA tips typically contain porous solid support which has derivatized antigens or antibodies covalently attached. Different analytes have different affinity for the tips so it is necessary to derivatize MSIA tips based on the analyte of interest.
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If the column is not properly equilibrated the desired molecule may not bind strongly to the column. The target analytes (anions or cations) are retained on the stationary phase but can be eluted by increasing the concentration of a similarly charged species that displaces the analyte ions from the stationary phase. For example, in cation exchange chromatography, the positively charged analyte can be displaced by adding positively charged sodium ions. The analytes of interest must then be detected by some means, typically by conductivity or UV/visible light absorbance.
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The method of standard additions is usually followed to eliminate matrix effects. Experimentally, equal volumes of the sample solution are taken, all but one are separately ‘spiked’ with known and different amounts of the analyte, and all are then diluted to the same volume. The instrument signals are then determined for all these solutions and the results plotted. As usual, the signal is plotted on the y-axis; in this case the x-axis is graduated in terms of the amounts of analyte added (either as an absolute weight or as a concentration).
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For magnetic particle separations a droplet of solution containing the analyte of interest is placed on a digital microfluidics electrode array and moved by the changes in the charges of the electrodes. The droplet is moved to an electrode with a magnet on one side of the array with magnetic particles functionalized to bind to the analyte. Then it is moved over the electrode, the magnetic field is removed and the particles are suspended in the droplet. The droplet is swirled on the electrode array to ensure mixing.
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Conversely, larger analytes spend little if any time in the pores and are eluted quickly. All columns have a range of molecular weights that can be separated.Range of molecular weights that can be separated for each packing material If an analyte is too large, it will not be retained; conversely, if the analyte is too small, it may be retained completely. Analytes that are not retained are eluted with the free volume outside of the particles (Vo), while analytes that are completely retained are eluted with volume of solvent held in the pores (Vi).
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Complexometric titrations rely on the formation of a complex between the analyte and the titrant. In general, they require specialized complexometric indicators that form weak complexes with the analyte. The most common example is the use of starch indicator to increase the sensitivity of iodometric titration, the dark blue complex of starch with iodine and iodide being more visible than iodine alone. Other complexometric indicators are Eriochrome Black T for the titration of calcium and magnesium ions, and the chelating agent EDTA used to titrate metal ions in solution.
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The FIDA principle is based on measuring the change in the apparent size (diffusivity) of a selective indicator interacting with the analyte molecule. The apparent indicator size is measured by Taylor dispersion analysis in a capillary under hydrodynamic flow.
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An example of a molecule that would be measured here is a metal-ligand complex. These monoliths operate in a similar method to the thin layer sol-gels in that they trap some analyte and show a color change.
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A dot blot is a special case of any of the above blots where the analyte is added directly to the blotting matrix (and appears as a "dot") as opposed to separating the sample by electrophoresis prior to blotting.
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McNeil's lab has produced gel-based sensors for mercury ions, nitrite ions, explosives, enzymes, and lead ions, which gel when the analyte is present. Many of the gels outperform current sensors for the same materials in sensitivity and in accuracy.
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HIDs are sensitive to a broad range of components. They must use helium as a carrier gas. HID is classified as a mass sensitive detector, which means that the analyte is destroyed during reaction. Therefore, it is considered a destructive detector.
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A potentiometric sensor is a type of chemical sensor that may be used to determine the analytical concentration of some components of the analyte gas or solution. These sensors measure the electrical potential of an electrode when no current is present.
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Permanganometry is one of the techniques used in chemical quantitative analysis. It is a redox titration that involves the use of permanganates to measure the amount of analyte present in unknown chemical samples.Redox titrations: Permanganometry. In: University Chemistry, Vol. 1.
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The direction of the analyte flow is determined by the respective concentration gradient and allows the usage of microdialysis probes as sampling as well as delivery tools. The solution leaving the probe (dialysate) is collected at certain time intervals for analysis.
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Previously a chart recorder and more recently a data logger or personal computer records the detector output as a function of time so that each sample output appears as a peak whose height depends on the analyte level in the sample.
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A known volume of a solution of acid can be standardized by titrating it against a solution of alkali of known concentration. Standard solutions are also commonly used to determine the concentration of an analyte species. By comparing the absorbance of the sample solution at a specific wavelength to a series of standard solutions at differing known as concentrations of the analyse species, the concentration of the sample solution can be found via Beer's Law. Any form of spectroscopy can be used in this way so long as the analyte species has substantial absorbance in the spectra.
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In the hybridization-ligation assay a template probe replaces the capture probe in the sandwich assay for immobilization to the solid support. The template probe is fully complementary to the oligonucleotide analyte and is intended to serve as a substrate for T4 DNA ligase-mediated ligation. The template probe has in addition an additional stretch complementary to a ligation probe so that the ligation probe will ligate onto the 3'-end of the analyte. Albeit generic, the ligation probe is similar to a detection probe in that it is labelled with, for example, digoxigenin for downstream signalling.
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One of the main reasons to use response factors is to compensate for the irreproducibility of manual injections into a gas chromatograph (GC). Injection volumes for GCs can be 1 microliter (µL) or less and are difficult to reproduce. Differences in the volume of injected analyte leads to differences in the areas of the peaks in the chromatogram and any quantitative results are suspect. To compensate for this error, a known amount of an internal standard (a second compound that does not interfere with the analysis of the primary analyte) is added to all solutions (standards and unknowns).
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This should allow the retention time of any such species under the analytical parameters of the assay to be determined. Any species causing a negative response may be considered to be contributing to ion suppression, but only if such species co-elute with the analyte of interest. It is also important to consider that species contributing to ion suppression may be retained by the column to a much greater extent than the analyte of interest. To this end, the detector response should be monitored for several times the usual chromatographic run time to ensure that ion suppression will not affect subsequent injections.
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The enzyme-linked immune absorbent spot (ELISpot) is a type of assay that focuses on quantitatively measuring the frequency of cytokine secretion for a single cell. The ELISpot Assay is also a form of immunostaining since it is classified as a technique that uses antibodies to detect a protein analyte, with the word analyte referring to any biological or chemical substance being identified or measured. The FluoroSpot Assay is a variation of the ELISpot assay. The FluoroSpot Assay uses fluorescence in order to analyze multiple analytes, meaning it can detect the secretion of more than one type of protein.
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As an analytical biochemistry assay and a "wet lab" technique, ELISA involves detection of an analyte (i.e., the specific substance whose presence is being quantitatively or qualitatively analyzed) in a liquid sample by a method that continues to use liquid reagents during the analysis (i.e., controlled sequence of biochemical reactions that will generate a signal which can be easily quantified and interpreted as a measure of the amount of analyte in the sample) that stays liquid and remains inside a reaction chamber or well needed to keep the reactants contained. This is in contrast to "dry lab" techniques that use dry strips.
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Titration NaOH HCl PP.ogv An acid–base titration is a method of quantitative analysis for determining the concentration of an acid or base by exactly neutralizing it with a standard solution of base or acid having known concentration. A pH indicator is used to monitor the progress of the acid–base reaction. If the acid dissociation constant (pKa) of the acid or base dissociation constant (PKb) of base in the analyte solution is known, its solution concentration (molarity) can be determined. Alternately, the pKa can be determined if the analyte solution has a known solution concentration by constructing a titration curve.
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Due to the constant perfusion of the microdialysis probe with fresh perfusate, a total equilibrium cannot be established. This results in dialysate concentrations that are lower than those measured at the distant sampling site. In order to correlate concentrations measured in the dialysate with those present at the distant sampling site, a calibration factor (recovery) is needed. The recovery can be determined at steady-state using the constant rate of analyte exchange across the microdialysis membrane. The rate at which an analyte is exchanged across the semipermeable membrane is generally expressed as the analyte’s extraction efficiency.
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1.5 J/cm² per Mol for NaCl, 2.5 J/cm² per Mol for (NH4)2SO4), and because the entropy of the analyte-solvent interface is controlled by surface tension, the addition of salts tend to increase the retention time. This technique is used for mild separation and recovery of proteins and protection of their biological activity in protein analysis (hydrophobic interaction chromatography, HIC). Another important factor is the mobile phase pH since it can change the hydrophobic character of the analyte. For this reason most methods use a buffering agent, such as sodium phosphate, to control the pH.
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This method requires an additional sample preparation step after the analyte extraction procedure has been completed (in this case SPE is preferentially used so common interferences can be removed from the sample). This additional step involves the derivatization of the YTXs with a fluorescent dienophile reagent — dimethoxy-4-methyl-3-oxo-3,4-dihydroquinoxalinyl)ethyl]-1,2,4-triazoline-3,5-dione, which facilitates analyte detection. This additional sample preparation step can make LC-FLD analysis extremely time-consuming and is a major disadvantage of the technique. ;Chromatographic methods coupled to mass spectrometry This technique is extremely useful for the analysis of multiple toxins.
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In negative-ion mode, the potential of the exit grid electrode can be set to negative potentials. Penning electrons undergo electron capture with atmospheric oxygen to produce O2−. The O2− will produce radical anions. Several reactions are possible, depending on the analyte.
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The resonance changes when biomolecules are captured or adsorbed on the sensor surface and depends on the concentration of the analyte as well as its properties. Surface plasmon resonance has been used in food quality and safety analysis, medical diagnostics, and environmental monitoring.
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Positive and negative ions of the analyte are formed by reactions with this plasma. For example, protonation occurs by :CH4 + e^- -> CH4+ + 2e^- (primary ion formation), :CH4 + CH4+ -> CH5+ + CH3 (reagent ion formation), :M + CH5+ -> CH4 + [M + H]+ (product ion formation, e.g. protonation).
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The volatile hydride generated by the reaction that occurs is swept into the atomization chamber by an inert gas, where it undergoes decomposition. This process forms an atomized form of the analyte, which can then be measured by absorption or emission spectrometry.
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Off-line analyte treatment process was time consuming and there was an inherent risk of sample contamination. Rapidly, it was realized that the analysis of complex mixtures would require the development of a fully automated on-line coupling solution in LC-MS.
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A rotating disk electrode (RDE) is a hydrodynamic working electrode used in a three electrode system.Bard, A.J.; Faulkner, L.R. Electrochemical Methods: Fundamentals and Applications. New York: John Wiley & Sons, 2nd Edition, 2000. The electrode rotates during experiments inducing a flux of analyte to the electrode.
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Ion exchange sorbents separate analytes based on electrostatic interactions between the analyte of interest and the positively or negatively charged groups on the stationary phase. For ion exchange to occur, both the stationary phase and sample must be at a pH where both are charged.
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100mM) are required to ensure that the analyte will be in a single ionic form. Otherwise, asymmetric peak shape, chromatographic tailing, and/or poor recovery from the stationary phase will be observed. For the separation of neutral polar analytes (e.g. carbohydrates), no buffer is necessary.
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Concentrations of a protein of interest in the samples can be obtained by comparing the fluorescent signals to those of a standard curve generated from a serial dilution of a known concentration of the analyte. Commonly also referred to as cytokine bead array (CBA).
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When only solvent is passing through the sample component the measured refractive index of both components is the same, but when an analyte passes through the flow cell the two measured refractive index are different. The difference appears as a peak in the chromatogram.
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In this case, the matrix may interfere with or attenuate the signal of the analyte. Therefore, a comparison between the standards (which contain no interfering compounds) and the unknown is not possible. The method of standard addition is a way to handle such a situation.
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The standard addition approach involves spiking the same sample extract with several known concentrations of analyte. This technique is more robust and effective than using matrix matched standards but is labor- intensive since each sample must be prepared several times to achieve a reliable calibration.
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However, a solvent without hydrogen, such as carbon tetrachloride, CCl4 or carbon disulfide, CS2, may also be used. Historically, deuterated solvents were supplied with a small amount (typically 0.1%) of tetramethylsilane (TMS) as an internal standard for calibrating the chemical shifts of each analyte proton.
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Combining time-resolved detection with pulsed powering results in additional benefits. In atomic emission, analyte atoms emit during different portions of the pulse than background atoms, allowing the two to be discriminated. Analogously, in mass spectrometry, sample and background ions are created at different times.
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However, in column chromatography, the retention factor or capacity factor (k) is defined as the ratio of time an analyte is retained in the stationary phase to the time it is retained in the mobile phase, which is inversely proportional to the retardation factor.
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Trends in Sample Preparation. Nova Publishers, 2006, p. 15-18. . In cases with complex or unknown matrices, the standard addition method can be used. In this technique, the response of the sample is measured and recorded, for example, using an electrode selective for the analyte.
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The resistance between the electrodes can be easily measured. The sensing material has an inherent resistance that can be modulated by the presence or absence of the analyte. During exposure, analytes interact with the sensing material. These interactions cause changes in the resistance reading.
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Upon binding of the analyte, changes in the electrostatic potential at the surface of the electrolyte-insulator layer occur, which in turn results in an electrostatic gating effect of the semiconductor device, and a measurable change in current between the source and drain electrodes.
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The analyte combines with its reciprocal ion in the IRP, this corresponds to retention time. Often organic salts are selected to pair with solute(s). The formation of this pair affects the interaction of the pair with the mobile phase and the stationary phase.
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Schematic of LSII Laserspray inlet ionization (LSII) is a subset of MAII and uses a matrix- assisted laser desorption/ionization (MALDI) method. It was originally called atmospheric pressure matrix-assisted laser desorption/ionization however was renamed as LSII to avoid confusion with MALDI and as it was found to be a type of inlet ionization. As all inlet ionization techniques, highly multiply charged ions are produced. A nitrogen laser is used to ablate the solid matrix/analyte into the heated inlet tube, the observed ions are generated at the surface of the matrix/analyte and so the laser is not directly involved in the ionization as was originally thought.
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A compass of molecular probes A molecular probe is a group of atoms or molecules used in molecular biology or chemistry to study the properties of other molecules or structures. If some measurable property of the molecular probe used changes when it interacts with the analyte (such as a change in absorbance), the interactions between the probe and the analyte can be studied. This makes it possible to indirectly study the properties of compounds and structures which may be hard to study directly. The choice of molecular probe will depend on which compound or structure is being studied as well as on what property is of interest.
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Atmospheric pressure chemical ionization interface A typical APCI usually consists of three main parts: a nebulizer probe which can be heated to 350-500 °C, an ionization region with a corona discharge needle, and an ion- transfer region under intermediate pressure. The analyte in solution is introduced from a direct inlet probe or a liquid chromatography (LC) eluate into a pneumatic nebulizer with a flow rate 0.2–2.0mL/min. In the heated nebulizer, the analyte coaxially flows with nebulizer N2 gas to produce a mist of fine droplets. By the combination effects of heat and gas flow, the emerged mist is converted into a gas stream.
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The fluorophore transduces the recognition event into a measurable optical signal. The use of extrinsic fluorophores, whose emission properties differ widely from those of the intrinsic fluorophores of proteins, tryptophan and tyrosine, enables one to immediately detect and quantify the analyte in complex biological mixtures. The integration of the fluorophore must be done in a site where it is sensitive to the binding of the analyte without perturbing the affinity of the receptor. Antibodies and artificial families of Antigen Binding Proteins (AgBP) are well suited to provide the recognition module of RF biosensors since they can be directed against any antigen (see the paragraph on bioreceptors).
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The potential is measured between the working electrode and the reference electrode, while the current is measured between the working electrode and the counter electrode. These data are plotted as current (i) versus applied potential (E, often referred to as just 'potential'). In Figure 2, during the initial forward scan (from t0 to t1) an increasingly reducing potential is applied; thus the cathodic current will, at least initially, increase over this time period assuming that there are reducible analytes in the system. At some point after the reduction potential of the analyte is reached, the cathodic current will decrease as the concentration of reducible analyte is depleted.
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Diagram showing the process of fast atom bombardment ionization of a solid sample dissolved in a matrixFast atom bombardment (FAB) is a method involving using a beam of high energy atoms to strike a surface and generate ions. These solid analyte particles must be dissolved into some form of matrix, or non-volatile liquid to protect and assist in the ionization of the solid analyte. It has been shown that as the matrix is depleted, the ion formation diminishes, so choosing the right matrix compound is vital. The overall goal of the matrix compound is to present the sample to the atom beam at a high mobile surface concentration.
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As well for the digestion in solution as for the in-gel digestion buffered solutions are needed, whose content in salts is too high and in analyte is too low for a successful ESI-MS measurement. Therefore, a combined desalting and concentration step is performed. Usually a reversed phase liquid chromatography is used, in which the peptides stay bound to the chromatography matrix whereas the salts are removed by washing. The peptides can be eluted from the matrix by the use of a small volume of a solution containing a large portion of organic solvent, which results in the reduction of the final volume of the analyte.
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In chemical ionization (CI) a reagent gas, typically methane or ammonia is introduced into the mass spectrometer. Depending on the technique (positive CI or negative CI) chosen, this reagent gas will interact with the electrons and analyte and cause a 'soft' ionization of the molecule of interest. A softer ionization fragments the molecule to a lower degree than the hard ionization of EI. One of the main benefits of using chemical ionization is that a mass fragment closely corresponding to the molecular weight of the analyte of interest is produced. In positive chemical ionization (PCI) the reagent gas interacts with the target molecule, most often with a proton exchange.
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Accelerated solvent extraction (ASE) is a method for extracting various chemicals from a complex solid or semisolid sample matrix. The process uses high temperature and pressure, which results in the extraction taking less time and requiring less solvent, and possibly also giving better analyte recovery, than traditional methods that use less extreme conditions. The elevated temperature is employed to increase extraction efficiency of the analyte of interest and the elevated pressure is used to keep the solvent in a liquid state as the temperature is increased above its boiling point. An automated system for the process was developed by Dionex, a company owned by Thermo Fisher Scientific.
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The (unweighted) regression line is calculated in the normal way, but space is provided for it to be extrapolated to the point on the x-axis at which y = 0. This negative intercept on the x-axis corresponds to the amount of the analyte in the test sample. This value is given by b/a, the ratio of the intercept and the slope of the regression line. Similarly in gas chromatography the following procedure is used: 1) The chromatogram of the unknown is recorded 2) a known amount of the analyte(s) of interest is added 3) the sample is analyzed again under the same conditions and the chromatogram is recorded.
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This is also similar to CI and the difference lies in the production of a radical cation with an odd number of electrons. The reagent gas molecules are bombarded with high energy electrons and the product reagent gas ions abstract electrons from the analyte to form radical cations. The common reagent gases used for this technique are toluene, benzene, NO, Xe, Ar and He. Careful control over the selection of reagent gases and the consideration toward the difference between the resonance energy of the reagent gas radical cation and the ionization energy of the analyte can be used to control fragmentation. The reactions for charge-exchange chemical ionization are as follows.
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Chemical ionization in an atmospheric pressure electric discharge is called atmospheric pressure chemical ionization (APCI), which usually uses water as the reagent gas. An APCI source is composed of a Liquid Chromatography outlet, nebulizing the eluent, a heated vaporizer tube, a corona discharge needle and a pinhole entrance to 10−3 torr vacuum. The analyte is a gas or liquid spray and ionization is accomplished using an atmospheric pressure corona discharge. This ionization method is often coupled with high performance liquid chromatography where the mobile phase containing eluting analyte sprayed with high flow rates of nitrogen or helium and the aerosol spray is subjected to a corona discharge to create ions.
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The signal is measured as the potential difference (voltage) between the working electrode and the reference electrode. The working electrode's potential must depend on the concentration of the analyte in the gas or solution phase. The reference electrode is needed to provide a defined reference potential.
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The conventional method generally uses a higher heating power and gas flow rate for the nebulizer gas, while also increasing the amount of dopant used during the technique. These increases can cause higher background noise, analyte interference, substrate impurities, and more ion reactions from excess dopant ions.
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N-Acetyltaurine can be quantified by a combination of high performance liquid chromatography and mass spectrometry (MS/MS). Due to the high hydrophilicity of N-acetyltaurine, the hydrophilic interaction chromatography (HILIC) is the method of choice in order to separate the analyte from the matrix components.
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Some common reagent gases include: methane, ammonia, and isobutane. Inside the ion source, the reagent gas is present in large excess compared to the analyte. Electrons entering the source will preferentially ionize the reagent gas. The resultant collisions with other reagent gas molecules will create an ionization plasma.
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But some of the manipulations may be inseparable part of the assay itself and will not thus be considered pre-analytic. # Target-specific DISCRIMINATION/IDENTIFICATION principle: to discriminate from background (noise) of similar components and specifically identify a particular target component ("analyte") in a biological material by its specific attributes. (e.g. in a PCR assay a specific oligonucleotide primer identifies the target by base pairing based on the specific nucleotide sequence unique to the target). # Signal (or target) AMPLIFICATION system: The presence and quantity of that analyte is converted into a detectable signal generally involving some method of signal amplification, so that it can be easily discriminated from noise and measured - e.g.
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The simulated moving bed (SMB) technique is a variant of high performance liquid chromatography; it is used to separate particles and/or chemical compounds that would be difficult or impossible to resolve otherwise. This increased separation is brought about by a valve-and-column arrangement that is used to lengthen the stationary phase indefinitely. In the moving bed technique of preparative chromatography the feed entry and the analyte recovery are simultaneous and continuous, but because of practical difficulties with a continuously moving bed, simulated moving bed technique was proposed. In the simulated moving bed technique instead of moving the bed, the sample inlet and the analyte exit positions are moved continuously, giving the impression of a moving bed.
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Antibodies have a high binding constant in excess of 10^8 L/mol, which stands for a nearly irreversible association once the antigen-antibody couple has formed. For certain analyte molecules like glucose affinity binding proteins exist that bind their ligand with a high specificity like an antibody, but with a much smaller binding constant on the order of 10^2 to 10^4 L/mol. The association between analyte and receptor then is of reversible nature and next to the couple between both also their free molecules occur in a measurable concentration. In case of glucose, for instance, concanavalin A may function as affinity receptor exhibiting a binding constant of 4x10^2 L/mol.
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Electrochemical biosensors are normally based on enzymatic catalysis of a reaction that produces or consumes electrons (such enzymes are rightly called redox enzymes). The sensor substrate usually contains three electrodes; a reference electrode, a working electrode and a counter electrode. The target analyte is involved in the reaction that takes place on the active electrode surface, and the reaction may cause either electron transfer across the double layer (producing a current) or can contribute to the double layer potential (producing a voltage). We can either measure the current (rate of flow of electrons is now proportional to the analyte concentration) at a fixed potential or the potential can be measured at zero current (this gives a logarithmic response).
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Depending on whether the reaction between the titrant and analyte is exothermic or endothermic, the temperature will either rise or fall during the titration. When all analyte has been consumed by reaction with the titrant, a change in the rate of temperature increase or decrease reveals the equivalence point and an inflection in the temperature curve can be observed. The equivalence point can be located precisely by employing the second derivative of the temperature curve. The software used in modern automated thermometric titration systems employ sophisticated digital smoothing algorithms so that "noise" resulting from the highly sensitive temperature probes does not interfere with the generation of a smooth, symmetrical second derivative "peak" which defines the endpoint.
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If the redox couple is reversible then during the reverse scan (from t1 to t2) the reduced analyte will start to be re-oxidized, giving rise to a current of reverse polarity (anodic current) to before. The more reversible the redox couple is, the more similar the oxidation peak will be in shape to the reduction peak. Hence, CV data can provide information about redox potentials and electrochemical reaction rates. For instance, if the electron transfer at the working electrode surface is fast and the current is limited by the diffusion of analyte species to the electrode surface, then the peak current will be proportional to the square root of the scan rate.
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Cyclic voltammetry (CV) has become an important and widely used electroanalytical technique in many areas of chemistry. It is often used to study a variety of redox processes, to determine the stability of reaction products, the presence of intermediates in redox reactions, electron transfer kinetics, and the reversibility of a reaction. CV can also be used to determine the electron stoichiometry of a system, the diffusion coefficient of an analyte, and the formal reduction potential of an analyte, which can be used as an identification tool. In addition, because concentration is proportional to current in a reversible, Nernstian system, the concentration of an unknown solution can be determined by generating a calibration curve of current vs. concentration.
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To choose the matrix for each solid analyte, three criteria must be considered. First, it should dissolve the solid compound to be analysed (with or without the aid of a cosolvent or additive), thus allowing molecules of that compound to diffuse to the surface layers, replenishing the sample molecules that have been ionized or destroyed by interaction with the fast atom beam. Another mechanism for explanation of ion formation in FAB involves the idea that sputtering occurs from the bulk rather than the surface, but in that case, the solubility is still largely important to insure homogeneity of solid analyte in the bulk solution. Secondly, the matrix should have a low volatility under the conditions of the mass spectrometer.
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If the sample cannot dissolve in the chosen matrix, such as glycerol, a cosolvent or additive can be mixed with the matrix to facilitate the dissolving of the solid analyte. For example, chlorophyll A is completely insoluble in glycerol, but by mixing in a small amount of Triton X-100, a derivative of polyethylene glycol, the chlorophyll becomes highly soluble within the matrix.product page from Shun Chia It is important to note that though a good signal may be achieved through glycerol or glycerol with an additive, there could be other matrix compounds that can offer an even better signal. Optimization of matrix compounds and concentration of solid analyte are vital for FAB measurements.
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Gravimetric analysis describes a set of methods used in analytical chemistry for the quantitative determination of an analyte (the ion being analyzed) based on its mass. The principle of this type of analysis is that once an ion's mass has been determined as a unique compound, that known measurement can then be used to determine the same analyte's mass in a mixture, as long as the relative quantities of the other constituents are known. The four main types of this method of analysis are precipitation, volatilization, electro- analytical and miscellaneous physical method. The methods involve changing the phase of the analyte to separate it in its pure form from the original mixture and are quantitative measurements.
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Nonequilibrium electrophoresis of equilibrated sample mixtures is generally used in the separation and study of binding interactions of large proteins and involves combining both the analyte and its receptor molecule in a premixed sample. These receptor molecules often take the form of affinity probes consisting of fluorophore-labeled molecules that will bind to target molecules that are mixed with the sample being tested. This mixture, and its subsequent complexes, are then separated through capillary electrophoresis. Because the original mixture of analyte and receptor molecule were bound together in an equilibrium, the slow dissociation of these two bound molecules during the electrophoretic experiment will result in their separation and a subsequent shift in equilibrium towards further dissociation.
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ERLIC (eHILIC) separations need not be isocratic, but the net effect is the reduction of the attraction of a particularly strong polar group, which then requires less strong elution conditions, and the enhanced interaction of the remaining polar (opposite charged ionic, or non-ionic) functional groups of the analyte(s).
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A high impedance voltmeter is used to measure the electromotive force or potential between the two electrodes when zero or no significant current flows between them. The potentiometric response is governed by the Nernst equation in that the potential is proportional to the logarithm of the concentration of the analyte.
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The reflective properties of the CD/DVD change based on the quantity of analyte in the sample. # The attenuated signal reaches the photodiode of the drive's pickup. # Analog signals are extracted, digitized, and converted to an image. The signal or optical density of the image is inversely proportional to concentration.
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CV can be conducted using a variety of solutions. Solvent choice for cyclic voltammetry takes into account several requirements. The solvent must dissolve the analyte and high concentrations of the supporting electrolyte. It must also be stable in the potential window of the experiment with respect to the working electrode.
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These ions are known as second-generation product ions. The radical cation products are then directed towards the mass analyzer by a repeller electrode. The ionization process often follows predictable cleavage reactions that give rise to fragment ions which, following detection and signal processing, convey structural information about the analyte.
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The idea of this procedure is that the total concentration of the analyte is the sum of the unknown and the standard, and that the total concentration varies linearly. If the signal response is linear in this concentration range, then a plot similar to what is shown above is generated.
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Photodissociation is used to detect electromagnetic activity of ions, compounds, and clusters when spectroscopy cannot be directly applied. Low concentrations of analyte can be one inhibiting factor to spectroscopy esp. in the gas phase. Mass spectrometers, time-of-flight and ion cyclotron resonance have been used to study hydrated ion clusters.
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The properties of a standard solution for titrations are: # Its concentration must remain constant all the time. This is so that there is no need for restandardization. # Its reaction with the analyte must be rapid in order to minimize the waiting period after addition of each reagent. # Its reaction must be reasonably complete.
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D-glycerate) in bodily fluids and tissues. D-glyceric acid can be measured in a laboratory that performs "analyte testing" for "organic acids" in blood (plasma) and urine. Symptoms of the disease (in its most severe form) include progressive neurological impairment, mental/motor retardation, hypotonia, seizures, failure to thrive and metabolic acidosis.
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A live-cell biosensor for cAMP can be used in non-lysed cells with the additional advantage of multiple reads to study the kinetics of receptor response. Nanobiosensors use an immobilized bioreceptor probe that is selective for target analyte molecules. Nanomaterials are exquisitely sensitive chemical and biological sensors. Nanoscale materials demonstrate unique properties.
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Spectral skewing is the change in relative intensity of mass spectral peaks due to the changes in concentration of the analyte in the ion source as the mass spectrum is scanned. This situation occurs routinely as chromatographic components elute into a continuous ion source.Watson, J. THrock, Sparkman,O David.Introduction to Mass Spectrometry.
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In chemical analysis, matrix refers to the components of a sample other than the analyte of interest. The matrix can have a considerable effect on the way the analysis is conducted and the quality of the results are obtained; such effects are called matrix effects.F. W. Fifield, P. J. Haines. Environmental Analytical Chemistry.
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In a study comparing the two types of separation, Isenberg, Brewer, Côté, and Striegel use both methods for polysaccharide characterization and conclude that HDC coupled with multiangle light scattering (MALS) achieves more accurate molar mass distribution when compared to off-line MALS than SEC in significantly less time. This is largely due to SEC being a more destructive technique because of the pores in the column degrading the analyte during separation, which tends to impact the mass distribution. However, the main disadvantage of HDC is low resolution of analyte peaks, which makes SEC a more viable option when used with chemicals that are not easily degradable and where rapid elution is not important. HDC plays an especially important role in the field of microfluidics.
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The rate at which the molecules progress along the column depends on the strength of adsorption, which in turn depends on the type of molecule and on the stationary phase materials. Since each type of molecule has a different rate of progression, the various components of the analyte mixture are separated as they progress along the column and reach the end of the column at different times (retention time). A detector is used to monitor the outlet stream from the column; thus, the time at which each component reaches the outlet and the amount of that component can be determined. Generally, substances are identified (qualitatively) by the order in which they emerge (elute) from the column and by the retention time of the analyte in the column.
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Also, resonance ionization is used for an atomic (elemental) analyte, whereas REMPI is used for a molecular analyte. The analytical technique on which the process of resonance ionization is based is termed resonance ionization mass spectrometry (RIMS). RIMS is derived from the original method, resonance ionization spectroscopy (RIS), which was initially being used to detect single atoms with better time resolution. RIMS has proved useful in the investigation of radioactive isotopes (such as for studying rare fleeting isotopes produced in high-energy collisions), trace analysis (such as for discovering impurities in highly pure materials), atomic spectroscopy (such as for detecting low-content materials in biological samples), and for applications in which high levels of sensitivity and elemental selectivity are desired.
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The equation can be shown as follows: :I^+=\beta Q_iL [\ce N] I_e The Ion extraction efficiency (β) can be optimized by increasing the voltage of both repeller and acceleration. Since the ionization cross section depends on the chemical nature of the sample and the energy of ionizing electrons a standard value of 70 eV is used. At low energies (around 20 eV), the interactions between the electrons and the analyte molecules do not transfer enough energy to cause ionization. At around 70 eV, the de Broglie wavelength of the electrons matches the length of typical bonds in organic molecules (about 0.14 nm) and energy transfer to organic analyte molecules is maximized, leading to the strongest possible ionization and fragmentation.
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The processes in a flame include the stages of desolvation (drying) in which the solvent is evaporated and the dry sample nano-particles remain, vaporization (transfer to the gaseous phase) in which the solid particles are converted into gaseous molecule, atomization in which the molecules are dissociated into free atoms, and ionization where (depending on the ionization potential of the analyte atoms and the energy available in a particular flame) atoms may be in part converted to gaseous ions. Each of these stages includes the risk of interference in case the degree of phase transfer is different for the analyte in the calibration standard and in the sample. Ionization is generally undesirable, as it reduces the number of atoms that are available for measurement, i.e., the sensitivity.
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Buffers serve multiple purposes: control of pH, neutralize the charge on the silica surface of the stationary phase and act as ion pairing agents to neutralize analyte charge. Ammonium formate is commonly added in mass spectrometry to improve detection of certain analytes by the formation of analyte-ammonium adducts. A volatile organic acid such as acetic acid, or most commonly formic acid, is often added to the mobile phase if mass spectrometry is used to analyze the column eluant. Trifluoroacetic acid is used infrequently in mass spectrometry applications due to its persistence in the detector and solvent delivery system, but can be effective in improving retention of analytes such as carboxylic acids in applications utilizing other detectors, as it is a fairly strong organic acid.
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When measuring the concentration of a solute in a supersaturated gaseous or liquid mixture it is obvious that the pressure inside the cuvette may be greater than the ambient pressure. When this is so a specialized cuvette must be used. The choice of analytical technique to use will depend on the characteristics of the analyte.
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Ionic additives, such as ammonium acetate and ammonium formate, are usually used to control the mobile phase pH and ion strength. In HILIC they can also contribute to the polarity of the analyte, resulting in differential changes in retention. For extremely polar analytes (e.g. aminoglycoside antibiotics (gentamicin) or Adenosine triphosphate), higher concentrations of buffer (ca.
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In most three electrode experiments there are two isolated cells. One contains the auxiliary and working electrode, while the other contains the reference electrode. Strictly speaking, the reference electrode does not require a separate compartment. A Quasi-Reference Electrode such as a silver/silver chloride wire electrode can be exposed directly to the analyte solution.
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In positive ion mode, DART produces predominantly protonated molecules [M+H]+ and in negative- ion mode deprotonated molecules [M-H]−. Both negative and positive modes of DART provides relatively simple mass spectra. Depending on the type of analyte, other species may be formed, such as multiple charged adducts. DART categorized under soft ionization technique.
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Propylene carbonate product may be converted to other carbonate esters by transesterification as well (see Carbonate ester#Carbonate transesterification).. In electrospray ionization mass spectrometry, propylene carbonate is doped into low surface tension solutions to increase analyte charging. In Grignard reaction propylene carbonate (or most other carbonate esters) might be used to create tertiary alcohols.
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The matrix absorbs energy from the laser pulse and transfers it to the analyte, causing desorption and ionization of the sample. MALDI generates [M+H]+ ions. DIOS was first reported by Gary Siuzdak, Jing Wei and Jillian M. Buriak in 1999. It was developed as a matrix-free alternative to MALDI for smaller molecules.
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Ion chromatogram displaying anion separation Ion-exchange chromatography separates molecules based on their respective charged groups. Ion-exchange chromatography retains analyte molecules on the column based on coulombic (ionic) interactions. The ion exchange chromatography matrix consists of positively and negatively charged ions. Essentially, molecules undergo electrostatic interactions with opposite charges on the stationary phase matrix.
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Similar to ISR, IDA also utilizes colorimetric (C-IDA) and fluorescence (F-IDA) indicators. In an IDA assay, a receptor is incubated with the indicator. When the analyte is added to the mixture, the indicator is released to the environment. Once the indicator is released it either changes color (C-IDA) or fluoresces (F-IDA).
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In the dopant- APPI mode, an easily ionizable compound (Dopant) is added to the mobile phase or the nebulizing gas to promote a reaction of charge-exchange between the dopant molecular ion and the analyte. The ionized sample is later transferred to the mass analyzer at high vacuum as it passes through small orifice skimmers.
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Inset figure shows analyte spectral features fit with VUV library olefin compound class spectral response information. The residual fit statistical data indicating a good fit is also shown. Compositional analysis of gasoline sample run using ASTM D8071. Carbon number and mass % or volume % composition of PIONA compounds are reported by VUV Analyze automated software.
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194, 404. . The most common approach for accounting for matrix effects is to build a calibration curve using standard samples with known analyte concentration and which try to approximate the matrix of the sample as much as possible. This is especially important for solid samples where there is a strong matrix influence.Marco Aurelio Zezzi Arruda.
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Then, a small volume of standard solution is added and the response is measured again. Ideally, the standard addition should increase the analyte concentration by a factor of 1.5 to 3, and several additions should be averaged. The volume of standard solution should be small enough to disturb the matrix as little as possible.
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The pH of the mobile phase can have an important role on the retention of an analyte and can change the selectivity of certain analytes. Charged analytes can be separated on a reversed-phase column by the use of ion-pairing (also called ion-interaction). This technique is known as reversed-phase ion-pairing chromatography.
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All chemosensors are designed to contain a signalling moiety and a recognition moiety. These are integrated directly or connected with a short covalent spacer depending on the mechanism involved in the signalling event. The chemosensor can be based on self- assembly of the sensor and the analyte. An example of such a design are the (indicator) displacement assays IDA.
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In the process of cation attachment, cations (typically H+ or Na+) attach themselves to analyte molecules; the desorption of the cation attachment (e.g., MNa+) can then be realized through the emitter heating and high field. The ionization of more polar organic molecules (e.g., ones with aliphatic hydroxyl or amino groups) in FD-MS typically go through this mechanism.
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Affinity chromatography is based on selective non-covalent interaction between an analyte and specific molecules. It is very specific, but not very robust. It is often used in biochemistry in the purification of proteins bound to tags. These fusion proteins are labeled with compounds such as His-tags, biotin or antigens, which bind to the stationary phase specifically.
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Randox developed the world's first biochip array technology (BAT) in 2002. BAT is a multi-analyte testing platform which allows simultaneous quantitative or qualitative detection of a wide range of analytes from a single patient sample. It screens biological samples in a rapid, accurate and easy-to-use format. £180 million was invested in research and development of BAT.
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Functionality modified probe tips has been to measure the binding force between single protein-ligand pairs. Probe tips have been used as a tapping mode technique to provide information about the elastic properties of materials. Probe tips are also used in the mass spectrometer. Enzymatically active probe tips have been used for the enzymatic degradation of analyte.
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APCI was applied to GC/MS and LC/MS also by Horning's group in 1975. Analyte in LC eluate was vaporized and ionized in a heated block. High sensitivity and simple mass spectra were obtained through this application. In the later decades, the coupling of APCI with LC/MS became famous and caught a lot attention.
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A biosensor is an analytical device, used for the detection of a chemical substance, that combines a biological component with a physicochemical detector. The sensitive biological element, e.g. tissue, microorganisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, etc., is a biologically derived material or biomimetic component that interacts with, binds with, or recognizes the analyte under study.
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Often the test items' properties and analyte concentrations are known to the organizer, but not disclosed to participants before the final report. However, there are also many schemes where the organizer doesn't know the sample composition. The participants' results are then compared to check if any participant had a bias towards e.g. higher values, or an unexpected imprecision.
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A pulsed Fourier-transform spectrometer does not employ transmittance techniques. In the most general description of pulsed FT spectrometry, a sample is exposed to an energizing event which causes a periodic response. The frequency of the periodic response, as governed by the field conditions in the spectrometer, is indicative of the measured properties of the analyte.
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Because MALDI uses a matrix, background ions are introduced due to ionization of the matrix. These ions reduce the usefulness of MALDI for small molecules. In contrast, DIOS uses a porous silicon surface to trap the analyte. This surface is not ionized by the laser, therefore creating minimal background ionization and thus allowing for the analysis of small molecules.
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Verpoorte's research explores simulating in vivo organismic biology onto microscopic external devices. This is achieved through fabrication and control of chemical detectors and separations modules onto silicon dioxide chips. This dramatically decreases the amount of analyte, solution, or cells required to perform a given analysis. Her specific interests involve electrokinetic control over movement of various substances on these chips.
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Later, these ions react with the analyte and transfer their charge. The sample ions then pass through small orifice skimmers by means of or ion-focusing lenses. Once inside the high vacuum region, the ions are subject to mass analysis. This interface can be operated in positive and negative charge modes and singly-charged ions are mainly produced.
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Separation occurs via the use of porous beads packed in a column (see stationary phase (chemistry)). Schematic of pore vs. analyte sizeThe smaller analytes can enter the pores more easily and therefore spend more time in these pores, increasing their retention time. These smaller molecules spend more time in the column and therefore will elute last.
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Currently, automated backpressure regulators can maintain a constant pressure in the column even if flow rate varies, mitigating this problem. A third drawback is difficulty in gas/liquid separation during collection of product. Upon depressurization, the CO2 rapidly turns into gas and aerosolizes any dissolved analyte in the process. Cyclone separators have lessened difficulties in gas/liquid separations.
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Calibrants can help circumvent this major drawback, however, these should be matched for size, charge and chemical class of the given analyte. An especially noteworthy variant is the "SUPER" IMS, which combines ion trapping by the so-called structures for lossless ion manipulations (SLIM) with several passes through the same drift region to achieve extremely high resolving powers.
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Typical titrations require titrant and analyte to be in a liquid (solution) form. Though solids are usually dissolved into an aqueous solution, other solvents such as glacial acetic acid or ethanol are used for special purposes (as in petrochemistry). Concentrated analytes are often diluted to improve accuracy. Many non- acid–base titrations require a constant pH during the reaction.
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Detailed sample preparation depends on the type of material. Pure standards are most likely to be prepared by chemical synthesis and purification and characterized by determination of remaining impurities. This is often done by commercial producers. Natural matrix CRMs (often shortened to 'matrix CRMs') contain an analyte or analytes in a natural sample (for, example, lead in fish tissue).
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The analyte will distribute between the phases according to its partition coefficient which is also called the distribution coefficient, distribution constant, or partition ratio and is represented by P, K, D, Kc, or KD. The partition coefficient for an analyte in a particular biphasic solvent system is independent of the volume of the instrument, flow rate, stationary phase retention volume ratio and the g-force required to immobilize the stationary phase. The degree of stationary phase retention is a crucial parameter. Common factors that influence stationary phase retention are flow rate, solvent composition of the biphasic solvent system, and the g-force. The stationary phase retention is represented by the stationary phase volume retention ratio (Sf) which is the volume of the stationary phase divided by the total volume of the instrument.
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Ionization at atmospheric pressure often leads to a loss of ions during the transfer of the ions from the ambient pressure region to the vacuum of the mass analyzer.Sheehan EW, Willoughby RC. June 13, 2006. U.S. Patent 7,060,976. Ions are lost due to dispersion of analyte spray and 'rim loss' causing fewer ions to reach the vacuum for m/z separation to occur.
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A typical mobile phase for HILIC chromatography includes acetonitrile ("MeCN", also designated as "ACN") with a small amount of water. However, any aprotic solvent miscible with water (e.g. THF or dioxane) can be used. Alcohols can also be used, however, their concentration must be higher to achieve the same degree of retention for an analyte relative to an aprotic solvent - water combination.
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Acoustic waves can be projected to the thin film to produce an oscillatory device, which then follows an equation that is nearly identical to the Sauerbrey equation used in the QCM method. Biomolecules, such as proteins or antibodies can bind and its change in mass gives a measureable signal proportional to the presence of the target analyte in the sample.
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DVDs are organized by sectors which each consist of 2064 bytes. A logical error correction code (ECC) block consists of 16 data sectors. The ECC block is the basic unit for testing disk quality by counting the number of parity inner errors (PIE) or parity inner failures (PIF). The software programs can analyze PIF density which is proportional to analyte concentration.
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The use of affinity binding receptors for purposes of biosensing has been proposed by Schultz and Sims in 1979 and was subsequently configured into a fluorescent assay for measuring glucose in the relevant physiological range between 4.4 and 6.1 mmol/L. The sensor principle has the advantage that it does not consume the analyte in a chemical reaction as occurs in enzymatic assays.
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A cloned enzyme donor immunoassay (CEDIA) is a competitive homogenous enzyme immunoassay. This assay makes use of two component fragments of an enzyme which are each individually inactive. Under the right conditions in solution these fragments can spontaneously reassemble to form the active enzyme. For use in biochemical assays one of the enzyme fragments is attached to an analyte of interest.
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Soxhlet extractor Extraction in chemistry is a separation process consisting in the separation of a substance from a matrix. Common examples include liquid-liquid extraction, and solid phase extraction. The distribution of a solute between two phases is an equilibrium condition described by partition theory. This is based on exactly how the analyte moves from the initial solvent into the extracting solvent.
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Soft laser desorption is a soft ionization technique which desorbs and ionizes molecules from surfaces with minimal fragmentation. This is useful for a broad range of small and large molecules and molecules that fragment easily. The first soft laser desorption techniques included Matrix- assisted laser desorption/ionization (MALDI) nanoparticles in glycerol. In MALDI, the analyte is first mixed with a matrix solution.
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Diagram of a MALDI ion source Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique. The sample is mixed with a matrix material. Upon receiving a laser pulse, the matrix absorbs the laser energy and it is thought that primarily the matrix is desorbed and ionized (by addition of a proton) by this event. The analyte molecules are also desorbed.
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It is common practice for 10% to 50% of the total number of samples to be used for QC purposes. The number of QC samples depends on the study objectives. The QC samples are used to address issues such as sample contamination and analyte recovery. The types of QC samples commonly used include; reagent blanks, field blanks, matrix spikes, and procedural spikes.
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The method of standard addition is used in instrumental analysis to determine concentration of a substance (analyte) in an unknown sample by comparison to a set of samples of known concentration, similar to using a calibration curve. Standard addition can be applied to most analytical techniques and is used instead of a calibration curve to solve the matrix effect problem.
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These particles are pushed through the drift tube by the carrier gas to the detection region. In this region, a beam of light crosses the column of analyte and the scattering of light is measured by a photodiode or photomultiplier tube. The detector's output is non-linear across more than one order of magnitude and proper calibration is required for quantitative analysis.
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Alternatively, pumps and sorbent tubes are placed in areas for fixed-point sampling. Chemicals are trapped onto the sorbent material throughout the sampling period. Occasionally, when desorbing the air sample from the sorbent tube, a large portion of the analyte will fail to go into the solution. In these cases, the sorbent tubes will have to be adjusted for desorption efficiency (DE).
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Electron Ionization of Methanol - Born Oppenheimer Potential Curves In this process, an electron from the analyte molecule (M) is expelled during the collision process to convert the molecule to a positive ion with an odd number of electrons. The following gas phase reaction describes the electron ionization processR. Davis, M. Frearson, (1987). Mass Spectrometry – Analytical Chemistry by Open Learning, John Wiley & Sons, London.
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The interaction strength depends on the functional groups part of the analyte molecular structure, with more polarized groups (e.g., hydroxyl-) and groups capable of hydrogen bonding inducing more retention. Coulombic (electrostatic) interactions can also increase retention. Use of more polar solvents in the mobile phase will decrease the retention time of the analytes, whereas more hydrophobic solvents tend to increase retention times.
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Panels combining 22,Razavi M, Anderson NL, Yip R, Pope ME, Pearson TW. Multiplexed longitudinal measurement of protein biomarkers in DBS using an automated SISCAPA workflow. Bioanalysis. 2016 Jul 15. 50,Whiteaker JR, Zhao L, Lin C, Yan P, Wang P, Paulovich AG. Sequential Multiplexed Analyte Quantification Using Peptide Immunoaffinity Enrichment Coupled to Mass Spectrometry. 2012 Jun 12;11(6):M111.015347–7.
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The current from the reduction of lead ion at the working electrode will decrease. The addition is repeated, and the current decreases again. A plot of the current against volume of added titrant will be a straight line. After enough titrant has been added to react completely with the analyte, the excess titrant may itself be reduced at the working electrode.
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In ESI the principle problem comes not from reactions in the gas phase but rather from problems involving the solution phase of the droplets themselves. Issues can be due to non-volatile substances remaining in the drops, which can change the efficiency of droplet formation or droplet evaporation, which in turn affects the amount of charged ions in the gas phase that ultimately reach the mass spectrometer. These problems can be fixed in multiple ways, including increasing the amount of concentration of analyte compared to matrix in the sample solution or by running the sample through a more extensive chromatographic technique before analysis. An example of a chromatographic technique that can aid in signal in ESI involves using 2-D liquid chromatography, or running the sample through two separate chromatography columns, giving better separation of the analyte from the matrix.
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The results can be read by flow cytometry because the beads are distinguishable by fluorescent signature. The number of analytes measured is determined by the number of different bead colors. Multiplex assays within a given application area or class of technology can be further stratified based on how many analytes can be measured per assay, where "multiplex" refers to those with the highest number of analyte measurements per assay (up to millions) and "low-plex" or "mid-plex" refers to procedures that process fewer (10s to 1000s), though there are no formal guidelines for calling a procedure multi-, mid-, or low- plex based on number of analytes measured. Single-analyte assays or low-to- mid-plex procedures typically predate the rise of their multiplex versions, which often require specialized technologies or miniaturization to achieve a higher degree of parallelization.
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The retention can be decreased by adding a less polar solvent (methanol, acetonitrile) into the mobile phase to reduce the surface tension of water. Gradient elution uses this effect by automatically reducing the polarity and the surface tension of the aqueous mobile phase during the course of the analysis. Structural properties of the analyte molecule play an important role in its retention characteristics. In general, an analyte with a larger hydrophobic surface area (C–H, C–C, and generally non-polar atomic bonds, such as S-S and others) is retained longer because it is non-interacting with the water structure. On the other hand, analytes with higher polar surface area (conferred by the presence of polar groups, such as -OH, -NH2, COO− or -NH3+ in their structure) are less retained as they are better integrated into water.
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The recognition moiety is responsible for binding to the analyte in a selective and reversible manner. If the binding sites are 'irreversible chemical reactions,' the indicators are described as fluorescent chemodosimeters, or fluorescent probes. An active communication pathway has to be open between the two moieties for the sensor to operate. In colorimetric chemosensors, this usually relies on the receptor and transducer to be structurally integrated.
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A rotating ring-disc electrode (RRDE)Albery W.J.; Hitchman M.L. Ring-Disc Electrodes Oxford: Clarendon Press 1971 () is a double working electrode used in hydrodynamic voltammetry, very similar to a rotating disk electrode (RDE).Bard, A.J.; Faulkner, L.R. Electrochemical Methods: Fundamentals and Applications. New York: John Wiley & Sons, 2nd Edition, 2000. The electrode rotates during experiments inducing a flux of analyte to the electrode.
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This is a frequently used technique in nuclear forensics. In this technique a purified sample is nebulized in a spray chamber and then aspirated into a plasma. The high temperature of the plasma leads to sample dissociation and high efficiency of ionization of the analyte. The ions then enter the mass spectrometer where they are discriminated based on mass based on a double focusing system.
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One advantage of using weirs is that the absence of posts allows more effective recycling of retenate for flow across the filter to wash off clogged cells. Magnetic beads are used to aid in analyte separation. These microscopic beads are functionalized with target molecules and moved through microfluidic channels using a varying magnetic field. This serves as a quick method of harvesting targets for analysis.
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Potentiometric sensors measure a potential or charge accumulation of an electrochemical cell. The transducer typically comprises an ion selective electrode (ISE) and a reference electrode. The ISE features a membrane that selectively interacts with the charged ion of interest, causing the accumulation of a charge potential compared to the reference electrode. The reference electrode provides a constant half-cell potential that is unaffected by analyte concentration.
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The device is based on detecting changes in absorption of a gold layer. A widely used research tool, the micro-array, can also be considered a biosensor. Biological biosensors often incorporate a genetically modified form of a native protein or enzyme. The protein is configured to detect a specific analyte and the ensuing signal is read by a detection instrument such as a fluorometer or luminometer.
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The number of particles in each stream can then be detected (in the case of proteins this is achieved by addition of an amine reactive fluorogenic dye). The ratio between the two streams is used to determine the diffusion co-efficient, which is used to calculate the hydrodynamic radius. The sum of particles in both streams can also be used to measure the concentration of the analyte.
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A total ionic strength adjustment buffer (TISAB) is a buffer solution which increases the ionic strength of a solution to a relatively high level. This is important for potentiometric measurements, including ion selective electrodes, because they measure the activity of the analyte rather than its concentration. TISAB essentially masks minor changes made in the ionic strength of the solution and hence increases the accuracy of the reading.
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Carbon nanotubes have been used to sense ionization of gaseous molecules while nanotubes made out of titanium have been employed to detect atmospheric concentrations of hydrogen at the molecular level. Some of these have been designed as field effect transistors, while others take advantage of optical sensing capabilities. Selective analyte binding is detected through spectral shift or fluorescence modulation. In a similar fashion, Flood et al.
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A Raman spectrum can be used to fingerprint a molecule, using incident light to excite Raman active vibrational modes irreversible scattering of photons. This creates a unique spectrum that can provide information on molecular shape. The spectrum obtained from an unknown analyte can be compared to the library of known spectra to identify any threats. Raman scattering is very weak, making detection difficult to enhancement is required.
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Volatilization is the process whereby a dissolved sample is vaporised. In atomic spectroscopy this is usually a two-step process. The analyte is turned into small droplets in a nebuliser which are entrained in a gas flow which is in turn volatilised in a high temperature flame in the case of AAS or volatilised in a gas plasma torch in the case of ICP spectroscopy.
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Chemical ionization (CI) is a lower energy process than electron ionization because it involves ion/molecule reactions rather than electron removal. The lower energy yields less fragmentation, and usually a simpler spectrum. A typical CI spectrum has an easily identifiable molecular ion. In a CI experiment, ions are produced through the collision of the analyte with ions of a reagent gas in the ion source.
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First, the sample is mixed with a suitable matrix material and applied to a metal plate. Second, a pulsed laser irradiates the sample, triggering ablation and desorption of the sample and matrix material. Finally, the analyte molecules are ionized by being protonated or deprotonated in the hot plume of ablated gases, and then they can be accelerated into whichever mass spectrometer is used to analyse them.
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The POCIS system is continually evaluated for the potential to sample a wide range of contaminants. Calibration data and analyte recovery methods are currently being generated by researchers around the world. Techniques to merge the POCIS device with bioassays are also under development. The POCIS sampler already serves as a versatile, economical, and robust tool for monitoring studies and observing trends in both space and time.
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Using the relationships defined by this equation, the diffusion coefficient of the electroactive species can be determined. Linear plots of ip vs. ν1/2 provide evidence for a chemically reversible redox process vs the cases where redox causes major structural change in the analyte. For species where the diffusion coefficient is known (or can be estimated), the slope of the plot of ip vs.
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Microdialysis probes manufactured by CMA Microdialysis AB, Kista, Sweden Microdialysis is a minimally-invasive sampling technique that is used for continuous measurement of free, unbound analyte concentrations in the extracellular fluid of virtually any tissue. Analytes may include endogenous molecules (e.g. neurotransmitter, hormones, glucose, etc.) to assess their biochemical functions in the body, or exogenous compounds (e.g. pharmaceuticals) to determine their distribution within the body.
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An important practical relevance of the phenomenon is as a type of interference that plagues certain immunoassays and nephelometric assays, resulting in false negatives or inaccurately low results. Other common forms of interference include antibody interference, cross-reactivity and signal interference. The phenomenon is caused by very high concentrations of a particular analyte or antibody and is most prevalent in one-step (sandwich) immunoassays.
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The TCD consists of an electrically heated filament in a temperature-controlled cell. Under normal conditions there is a stable heat flow from the filament to the detector body. When an analyte elutes and the thermal conductivity of the column effluent is reduced, the filament heats up and changes resistance. This resistance change is often sensed by a Wheatstone bridge circuit which produces a measurable voltage change.
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Spiropyrans can be used to probe the conformational state of DNA, as certain derivatives can intercalate into DNA when in the open form. Spiropyrans are used in photo controlled transfer of amino acids across bilayers and membranes because of nucleophilic interaction between zwitterionic merocyanine and polar amino acids. Certain types of spiropyrans display ring opening upon recognition of an analyte, for example zinc ions.
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An optode requires three components to function: a chemical that responds to an analyte, a polymer to immobilise the chemical transducer and instrumentation (optical fibre, light source, detector and other electronics). Optodes usually have the polymer matrix coated onto the tip of an optical fibre, but in the case of evanescent wave optodes the polymer is coated on a section of fibre that has been unsheathed.
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As it is only effective for primary amines, the carbylamine reaction can be used as a chemical test for their presence. In this context, the reaction is also known as Saytzeff's isocyanide test.Carbylamine reaction In this reaction, the analyte is heated with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide (carbylamine) is formed, as indicated by a foul odour.
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Only certain types of isotopes of certain elements show up in NMR spectra. Only these isotopes cause NMR coupling. Nuclei of atoms having the same equivalent positions within a molecule also do not couple with each other. 1H (proton) NMR spectroscopy and 13C NMR spectroscopy analyze 1H and 13C nuclei, respectively, and are the most common types (most common analyte isotopes which show signals) of NMR spectroscopy.
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Diagram which depicts the basics of flow injection analysis A sample (analyte) is injected into a flowing carrier solution stream that is forced by a peristaltic pump. The injection of the sample is done under controlled dispersion in known volumes. The carrier solution and sample then meet at mixing points with reagents and react. The reaction time is controlled by a pump and reaction coil.
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Bio-FETs couple a transistor device with a bio-sensitive layer that can specifically detect bio-molecules such as nucleic acids and proteins. A Bio-FET system consists of a semiconducting field-effect transistor that acts as a transducer separated by an insulator layer (e.g. SiO2) from the biological recognition element (e.g. receptors or probe molecules) which are selective to the target molecule called analyte.
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A schematic diagram of chemical ionization source Chemical ionization (CI) is a soft ionization technique used in mass spectrometry. This was first introduced by Burnaby Munson and Frank H. Field in 1966. This technique is a branch of gaseous ion-molecule chemistry. Reagent gas molecules are ionized by electron ionization, which subsequently react with analyte molecules in the gas phase in order to achieve ionization.
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Liquid–liquid extraction or solvent extraction can be used to isolate YTXs from the sample medium. Methanol is normally the solvent of choice, but other solvents can also be used including acetone and chloroform. The drawback of using the solvent extraction method is the levels of analyte recovery can be poor, so any results obtained from the quantification processes may not be representative of the sample.
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Electrons entering the source with energy around 200-500 eV will preferentially ionize the reagent gas. Then, the ion/molecule reactions produces more stable reagent ions and the resultant collisions with other reagent gas molecules will create an ionization plasma. Positive and negative ions of the analyte are formed by reactions with this plasma. The following reactions are possible with methane as the reagent gas.
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The high energy molecular ions produced by the bombardment with electrons pass their energy to neutral molecules via collision. This allows the analytes to be less fragmented and therefore molecular weight of an unknown analyte can be determined. The extent of fragmentation is controlled by proper selection of reagent gases. The spectra given by CI is simpler and more sensitive compared to other ionization methods.
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FIA is an automated method of chemical analysis in which a sample is injected into a flowing carrier solution that mixes with reagents before reaching a detector. Over past 30 years, FIA techniques developed into a wide array of applications using spectrophotometry, fluorescence spectroscopy, atomic absorption spectroscopy, mass spectrometry, and other methods of instrumental analysis for detection. Automated sample processing, high repeatability, adaptability to micro-miniaturization, containment of chemicals, waste reduction, and reagent economy in a system that operates at microliter levels are all valuable assets that contribute to the application of flow injection to real- world assays. The main assets of flow injection are the well defined concentration gradient that forms when an analyte is injected into the reagent stream (which offers an infinite number of well-reproduced analyte/reagent ratios) and the exact timing of fluidic manipulations (which provide exquisite control over the reaction conditions).
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Other receptors are sensitive not to a specific molecule but to a molecular compound class, these chemosensors are used in array- (or microarray) based sensors. Array-based sensors utilise analyte binding by the differential receptors. One example is the grouped analysis of several tannic acids that accumulate in ageing Scotch whisky in oak barrels. The grouped results demonstrated a correlation with the age but the individual components did not.
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Electrochemical sensors can used for label-free sensing of biomolecules. They detect changes and measure current between a probed metal electrode and an electrolyte containing the target analyte. A known potential to the electrode is then applied from a feedback current and the resulting current can be measured. For example, one technique using electrochemical sensing includes slowly raising the voltage causing chemical species at the electrode to be oxidized or reduced.
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In FD, the analyte is applied as a thin film directly to the emitter, or small crystals of solid materials are placed onto the emitter. Slow heating of the emitter then begins, by passing a high current through the emitter, which is maintained at a high potential (e.g. 5 kilovolts). As heating of the emitter continues, low- vapor pressure materials get desorbed and ionized by alkali metal cation attachment.
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Optical biotransducers, used in optical biosensors for signal transduction, use photons in order to collect information about analyte.Sergey M. Borisov, Otto S. Wolfbeis, Optical Biosensors, Chemical Reviews, 2008, Vol. 108, No. 2 These are highly sensitive, highly specific, small in size and cost effective. The detection mechanism of optical biotransducer depends upon the enzyme system that converts analyte into products which are either oxidized or reduced at the working electrode.
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A blank solution is a solution containing little to no analyte of interest, usually used to calibrate instruments such as a colorimeter. According to the EPA, the "primary purpose of blanks is to trace sources of artificially introduced contamination." Different types of blanks are used to identify the source of contamination in the sample. The types of blanks include equipment blank, field blank, trip blank, method blank, and instrument blank.
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A differential refractometer (DRI), or refractive index detector (RI or RID) is a detector that measures the refractive index of an analyte relative to the solvent. They are often used as detectors for high-performance liquid chromatography and size exclusion chromatography. They are considered to be universal detectors because they can detect anything with a refractive index different from the solvent, but they have low sensitivity.Undergraduate Instrumental Methods of Analysis.
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Detailed procedures for the cobalt thiocyanate test are available. The reagent consists of 2% cobalt thiocyanate dissolved in dilute acid. Glycerol is often added to stabilise the cobalt complex, ensuring it only goes blue when in contact with an analyte and not due to drying. Addition of the cobalt thiocyanate reagent to cocaine hydrochloride results in the surface of the particles turning a bright blue (faint blue for cocaine base).
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Schematic of band structures of metals, semiconductors, quantum dots (QD) and single. Graphic illustrating the change in QD band gap and photoluminescence emission wavelength, or color, with increasing particle size. Properties of nanoparticles can be altered through nanoparticle-ligand systems which are targeted to specific analytes. Electromagnetic properties of nanosponges can be altered by analyte binding to be used as a transducer in chemical sensing systems, specifically for explosive analytes.
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The test is accomplished by wiping a small moist wiping fleece on a surface, or on the forehead, palm, or tongue of an individual. An integrated ampule is then broken which acts as the medium for transporting the collected analyte to the antigen binding site. The DrugWipe can be configured to detect cannabis, cocaine, opiates, amphetamines, MDMA, and benzodiazepines. Immunoassay strips containing antibodies bind to components of the different drugs.
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The excited analyte atoms emit light at characteristic wavelengths that can be dispersed with a monochromator and detected. In the past, the spark or arc conditions were typically not well controlled, the analysis for the elements in the sample were qualitative. However, modern spark sources with controlled discharges can be considered quantitative. Both qualitative and quantitative spark analysis are widely used for production quality control in foundry and metal casting facilities.
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Schematic of LSII Due to recent innovations to the laser spray technique, a new method of laser ablation using the spray method has surfaced. Laserspray inlet ionization (LSII) involves a matrix/analyte sample at atmospheric pressure being ablated, and the ionization process will take place in an ion transfer capillary tube located in the mass spectrometer inlet. The LSII method is also known as laserspray ionization vacuum (LSIV).
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Instrumental methods may be used to separate samples using chromatography, electrophoresis or field flow fractionation. Then qualitative and quantitative analysis can be performed, often with the same instrument and may use light interaction, heat interaction, electric fields or magnetic fields. Often the same instrument can separate, identify and quantify an analyte. Analytical chemistry is also focused on improvements in experimental design, chemometrics, and the creation of new measurement tools.
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Hence, the mass spectrum of a sample is a pattern representing the distribution of ions by mass (more correctly: mass-to-charge ratio) in a sample. It is a histogram usually acquired using an instrument called a mass spectrometer. Not all mass spectra of a given substance are the same. For example, some mass spectrometers break the analyte molecules into fragments; others observe the intact molecular masses with little fragmentation.
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The stationary phase consists of an immobile matrix that contains charged ionizable functional groups or ligands. The stationary phase surface displays ionic functional groups (R-X) that interact with analyte ions of opposite charge. To achieve electroneutrality, these inert charges couple with exchangeable counterions in the solution. Ionizable molecules that are to be purified compete with these exchangeable counterions for binding to the immobilized charges on the stationary phase.
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Solution- phase Raman spectroscopy often results in a weak scattering cross-section. Therefore, recent advances have been made to enhance the Raman signals, such as surface enhanced Raman spectroscopy, and Resonance Raman spectroscopy. Such techniques serve an additional purpose of quantifying the analyte-receptor binding events, giving a more detailed picture of the host–guest complexation phenomena where they actually take place; in solutions. In a recent breakthrough, Flood et al.
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An alternative to measure BOD is the development of biosensors, which are devices for the detection of an analyte that combines a biological component with a physicochemical detector component. Enzymes are the most widely used biological sensing elements in the fabrication of biosensors. Their application in biosensor construction is limited by the tedious, time- consuming and costly enzyme purification methods. Microorganisms provide an ideal alternative to these bottlenecks.
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The magnet is reintroduced and the particles are immobilized and the droplet is moved away. This process is repeated with wash and elution buffers to extract the analyte. Magnetic particles coated with antihuman serum albumin antibodies have been used to isolate human serum albumin, as proof of concept work for immunoprecipitation using digital microfluidics.5 DNA extraction from a whole blood sample has also been performed with digital microfluidics.
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GC-VUV bulk compound characterization was first applied to the analysis of paraffin, isoparaffin, olefin, naphthene, and aromatic (PIONA) hydrocarbons in gasoline streams. It is suitable for use with finished gasoline, reformate, reformer feed, FCC, light naphtha, and heavy naphtha samples. A typical chromatographic analysis is displayed in Figure 7. The inset shows how the analyte spectral response is fit with VUV library spectra for the selected time slice.
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SBCADD is included as a secondary target condition in most newborn screening programs, as the key analyte is the same as is used to identify isovaleric acidemia. Most cases have been Hmong individuals, who are asymptomatic. There are isolated case reports where individuals have been identified with SBCADD in addition to developmental delay and epilepsy. It is currently unclear what the complete clinical presentation of SBCADD looks like.
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AUC is a method by which for a given peptide spectrum in an LC-MS run, the area under the spectral peak is calculated. AUC peak measurements are linearly proportional to the concentration of protein in a given analyte mixture. Quantification is achieved with through ion counts, the measurement of the amount of an ion at a specific retention time. Discretion is required for the standardization of the raw data.
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Ion cyclotron resonance is a phenomenon related to the movement of ions in a magnetic field. It is used for accelerating ions in a cyclotron, and for measuring the masses of an ionized analyte in mass spectrometry, particularly with Fourier transform ion cyclotron resonance mass spectrometers. It can also be used to follow the kinetics of chemical reactions in a dilute gas mixture, provided these involve charged species.
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Analyte molecules partition between a liquid stationary phase and the eluent. Just as in Hydrophilic Interaction Chromatography (HILIC; a sub-technique within HPLC), this method separates analytes based on differences in their polarity. HILIC most often uses a bonded polar stationary phase and a mobile phase made primarily of acetonitrile with water as the strong component. Partition HPLC has been used historically on unbonded silica or alumina supports.
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Tubing on a nano-liquid chromatography (nano-LC) system, used for very low flow capacities. The internal diameter (ID) of an HPLC column is an important parameter that influences the detection sensitivity and separation selectivity in gradient elution. It also determines the quantity of analyte that can be loaded onto the column. Larger columns are usually seen in industrial applications, such as the purification of a drug product for later use.
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Simplified schematic of a single gap chemiresistive sensor. (not to scale) A chemiresistor is a material that changes its electrical resistance in response to changes in the nearby chemical environment.Florinel-Gabriel Banica, Chemical Sensors and Biosensors: Fundamentals and Applications, John Wiley and Sons, Chichester, 2012, chapter 11, Print ; Web ; . Chemiresistors are a class of chemical sensors that rely on the direct chemical interaction between the sensing material and the analyte.
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Capillary electrochromatography (CEC) is an electrochromatography technique in which the liquid mobile phase is driven through a capillary containing the chromatographic stationary phase by electroosmosis. It is a combination of high-performance liquid chromatography and capillary electrophoresis. The capillaries is packed with HPLC stationary phase and a high voltage is applied to achieve separation is achieved by electrophoretic migration of the analyte and differential partitioning in the stationary phase.
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Although the concept of using a single optical element for analyte regression and detection was suggested in 1986, the first full MOC concept device was published in 1997 from the Myrick group at the University of South Carolina, with a subsequent demonstration in 2001. The technique has received much recognition in the optics industry as a new method to perform optical analysis with advantages for harsh environment sensing.Myrick, M.L. (2002). "Multivariate optical elements simplify spectroscopy".
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Bulk electrolysis is also known as potentiostatic coulometry or controlled potential coulometry. The experiment is a form of coulometry which generally employs a three electrode system controlled by a potentiostat. In the experiment the working electrode is held at a constant potential (volts) and current (amps) is monitored over time (seconds). In a properly run experiment an analyte is quantitatively converted from its original oxidation state to a new oxidation state, either reduced or oxidized.
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They have only two electrodes and are extremely sensitive and robust. They enable the detection of analytes at levels previously only achievable by HPLC and LC/MS and without rigorous sample preparation. All biosensors usually involve minimal sample preparation as the biological sensing component is highly selective for the analyte concerned. The signal is produced by electrochemical and physical changes in the conducting polymer layer due to changes occurring at the surface of the sensor.
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The first stage of the instrument is an ion source where samples are converted to gas phase ions. Many ionization methods similar to those traditionally used for mass spectrometry have been employed for IM-MS depending on the physical state of the analyte. Gas phase samples are typically ionized with thermal desorption, radioactive ionization, corona discharge ionization and photoionization techniques. Electrospray ionization and secondary electrospray ionization (SESI) are common methods for ionizing samples in solution.
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The inner surface of the microfluidic channels is composed of polyethylene terephthalate, to which the PEG-b/pNIPAAm beads reversibly bind above the LCST. When the sample solution is passed through the channels, the target analyte binds to the biotin ligand. The temperature can then be brought below the LCST to dissociate and become removed from the inner channels. This allows for a system adept to being reloaded with stationary phase under mild conditions.
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The nitrogen–phosphorus detector (NPD) is also known as thermionic specific detector (TSD) is a detector commonly used with gas chromatography, in which thermal energy is used to ionize an analyte. It is a type of flame thermionic detector (FTD), the other being the alkali flame-ionization detector (AFID also known as AFD). With this method, nitrogen and phosphorus can be selectively detected with a sensitivity that is 104 times greater than that for carbon.
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In magnetic spectroscopy (EPR, NMR), a microwave pulse (EPR) or a radio frequency pulse (NMR) in a strong ambient magnetic field is used as the energizing event. This turns the magnetic particles at an angle to the ambient field, resulting in gyration. The gyrating spins then induce a periodic current in a detector coil. Each spin exhibits a characteristic frequency of gyration (relative to the field strength) which reveals information about the analyte.
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The FluoroSpot assay is very similar to the ELISpot assay. The main difference is that the FluoroSpot assay is able to analyze the presence of multiple analytes on one plate of wells, whereas the ELISpot assay can only analyze one analyte at a time. The FluoroSpot assay accomplishes this by using fluorescence rather than an enzymatic reaction for detection. The steps for a FluoroSpot assay are also similar, with a few differences.
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The waveform of even reversible couples is complex owing to the combined effects of polarization and diffusion. The difference between the two peak potentials (Ep), ΔEp, is of particular interest. : ΔEp = Epa \- Epc > 0 This difference mainly results from the effects of analyte diffusion rates. In the ideal case of a reversible 1e- couple, ΔEp is 57 mV and the full-width half-max of the forward scan peak is 59 mV.
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Sample preparation for PI includes first ensuring the sample is in the gas phase. PI ionizes molecules by exciting the sample molecules with photons of light. This method only works if the sample and other components in the gas phase are excited by different wavelengths of light. It is important when preparing the sample, or photon source, that the wavelengths of ionization are adjusted to excite the sample analyte and nothing else.
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In LC-MS the desalting/concentration is realised with a pre-column, in off-line measurements reversed phase micro columns are used, which can be used directly with microliter pipettes. Here, the peptides are eluted with the spray solution containing an appropriate portion of organic solvent. The resulting solution (usually a few microliters) is enriched with the analyte and, after transfer to the spray capillary, can be directly used in the MS.
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A major advantage of the DME is that each drop has a smooth and uncontaminated surface free from any adsorbed analyte or impurity. The self-renewing electrode does not need to be cleaned or polished like a solid electrode. This advantage comes at the cost of a working electrode with a constantly changing surface area. Since the drops are produced predictably the changing surface area can be accounted for or even used advantageously.
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The source for APCI is similar to ESI except that ions are formed by the interaction of the heated analyte solvent with a corona discharge needle set at a high electrical potential. Primary ions are formed immediately surrounding the needle, and these interact with the solvent to form secondary ions that ultimately ionize the sample. APCI is particularly useful for the analysis of nonpolar lipids such as triacylglycerols, sterols, and fatty acid esters.
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In volatilization methods, removal of the analyte involves separation by heating or chemically decomposing a volatile sample at a suitable temperature. In other words, thermal or chemical energy is used to precipitate a volatile species. For example, the water content of a compound can be determined by vaporizing the water using thermal energy (heat). Heat can also be used, if oxygen is present, for combustion to isolate the suspect species and obtain the desired results.
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ELSDs analyze solvent after elution from HPLC. As the eluent passes from an HPLC, it is mixed with an inert carrier gas and forced through a nebulizer, which separates the liquid into minute aerosolized droplets. These droplets then pass into a heated drift tube, where the mobile phase solvent is evaporated off. As the mobile phase evaporates, the droplets become smaller and smaller until all that is left is minute particles of dried analyte.
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Identification tests are conducted to ensure the identity of an analyte in a sample through comparison of the sample to a reference standard through methods such as spectrum, chromatographic behavior, and chemical reactivity. Impurity testing can either be a quantitative test or a limit test. Both tests should accurately measure the purity of the sample. Quantitative tests of either the active moiety or other components of a sample can be conducted through assay procedures.
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This small molecule probe is water-soluble, and operates in the blue-green region of the spectrum. Saccharide recognition in our probe system is achieved with a boronic acids appended viologen that serves as an analyte responsive fluorescence quencher. We used an anionic dye which forms a weakly fluorescent complex with the cationic viologen receptor. At and near physiological pH, saccharide binding by the receptor results in a partial charge neutralization of the viologen.
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In electrochemistry, the Cottrell equation describes the change in electric current with respect to time in a controlled potential experiment, such as chronoamperometry. Specifically it describes the current response when the potential is a step function in time. It was derived by Frederick Gardner Cottrell in 1903. For a simple redox event, such as the ferrocene/ferrocenium couple, the current measured depends on the rate at which the analyte diffuses to the electrode.
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Biological separations usually involve low concentration high volume samples. This can pose an issue for digital microfluidics due to the small sample volume necessary. Digital microfluidic systems can be combined with a macrofluidic system designed to decrease sample volume, in turn increasing analyte concentration. It follows the same principles as the magnetic particles for separation, but includes pumping of the droplet to cycle a larger volume of fluid around the magnetic particles.
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Choosing the appropriate matrix for the sample is crucial because the matrix can also influence the degree of fragmentation of the sample (analyte) ions. The sample can then be introduced to FAB analysis. The normal method of introducing the sample-matrix mixture is through an insertion probe. The sample-matrix mixture is loaded on a stainless steel sample target on the probe, which is then placed in the ion source via a vacuum lock.
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Each works effectively for separating analytes by relative polar differences. HILIC bonded phases have the advantage of separating acidic, basic and neutral solutes in a single chromatographic run. from review The polar analytes diffuse into a stationary water layer associated with the polar stationary phase and are thus retained. The stronger the interactions between the polar analyte and the polar stationary phase (relative to the mobile phase) the longer the elution time.
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The sensing material and the analyte can interact by covalent bonding, hydrogen bonding, or molecular recognition. Several different materials have chemiresistor properties: metal-oxide semiconductors, some conductive polymers, and nanomaterials like graphene, carbon nanotubes and nanoparticles. Typically these materials are used as partially selective sensors in devices like electronic tongues or electronic noses. A basic chemiresistor consists of a sensing material that bridges the gap between two electrodes or coats a set of interdigitated electrodes.
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Skin based analyte detection is now possible without damaging and continuous replacing of the electrodes as this paper will be immune to sweat. With its endless applications this field of material science is sure to be more explored. A recent application of hydrophobic structures and materials is in the development of micro fuel cell chips. Reactions within the fuel cell produce waste gas CO2 which can be vented out through these hydrophobic membranes.
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In this case it is normally quantified by comparing the assays response to a range of similar analytes and expressed as a percentage. In practice, calibration curves are produced using fixed concentration ranges for a selection of related compounds and the midpoints (IC50) of the calibration curves are calculated and compared. The figure then provides an estimate of the response of the assay to possible interfering compounds relative to the target analyte.
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The technique gives a limit of detection (LOD) of 0.3 μg/ml and a limit of quantification (LOQ)of 0.9 μg/ml. The sensitivity of conventional CEUV can be improved by using micellar electrokinetic chromatography (MEKC). CEMS has the added advantage over CEUV of being able to give molecular weight and/or structural information about the analyte. This enables the user to carry out unequivocal confirmations of the analytes present in the sample.
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Nanoparticles may assist in detecting trace levels of contaminants in field settings, contributing to effective remediation. Instruments that can operate outside of a laboratory often are not sensitive enough to detect trace contaminants. Rapid, portable, and cost- effective measurement systems for trace contaminants in groundwater and other environmental media would thus enhance contaminant detection and cleanup. One potential method is to separate the analyte from the sample and concentrate them to a smaller volume, easing detection and measurement.
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The sample is then added to the cartridge. As the sample passes through the stationary phase, the polar analytes in the sample will interact and retain on the polar sorbent while the solvent, and other non- polar impurities pass through the cartridge. After the sample is loaded, the cartridge is washed with a non-polar solvent to remove further impurities. Then, the analyte is eluted with a polar solvent or a buffer of the appropriate pH.
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The distribution constant (or partition ratio) (KD) is the equilibrium constant for the distribution of an analyte in two immiscible solvents.IUPAC Definition of partition ratio In chromatography, for a particular solvent, it is equal to the ratio of its molar concentration in the stationary phase to its molar concentration in the mobile phase, also approximating the ratio of the solubility of the solvent in each phase. The term is often confused with partition coefficient or distribution coefficient.
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Biosensors are devices that consist of a biological recognition system, called the bioreceptor, and a transducer. The interaction of the analyte with the bioreceptor causes an effect that the transducer can convert into a measurement, such as an electrical signal. The most common bioreceptors used in biosensing are based on antibody–antigen interactions, nucleic acid interactions, enzymatic interactions, cellular interactions, and interactions using biomimetic materials. Common transducer techniques include mechanical detection, electrical detection, and optical detection.
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DNA can be the analyte of a biosensor, being detected through specific means, but it can also be used as part of a biosensor or, theoretically, even as a whole biosensor. Many techniques exist to detect DNA, which is usually a means to detect organisms that have that particular DNA. DNA sequences can also be used as described above. But more forward-looking approaches exist, where DNA can be synthesized to hold enzymes in a biological, stable gel.
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The biologically sensitive elements can also be created by biological engineering. The transducer or the detector element, which transforms one signal into another one, works in a physicochemical way: optical, piezoelectric, electrochemical, electrochemiluminescence etc., resulting from the interaction of the analyte with the biological element, to easily measure and quantify. The biosensor reader device connects with the associated electronics or signal processors that are primarily responsible for the display of the results in a user- friendly way.
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Piezoelectric sensors utilise crystals which undergo an elastic deformation when an electrical potential is applied to them. An alternating potential (A.C.) produces a standing wave in the crystal at a characteristic frequency. This frequency is highly dependent on the elastic properties of the crystal, such that if a crystal is coated with a biological recognition element the binding of a (large) target analyte to a receptor will produce a change in the resonance frequency, which gives a binding signal.
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In particular, phosphorus emission is around 510–536 nm and sulfur emission is at 394 nm. With an atomic emission detector (AED), a sample eluting from a column enters a chamber which is energized by microwaves that induce a plasma. The plasma causes the analyte sample to decompose and certain elements generate an atomic emission spectra. The atomic emission spectra is diffracted by a diffraction grating and detected by a series of photomultiplier tubes or photo diodes.
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Traditional ELISA typically involves chromogenic reporters and substrates that produce some kind of observable color change to indicate the presence of antigen or analyte. Newer ELISA-like techniques use fluorogenic, electrochemiluminescent, and quantitaoppositiontive PCR reporters to create quantifiable signals. These new reporters can have various advantages, including higher sensitivities and multiplexing. In technical terms, newer assays of this type are not strictly ELISAs, as they are not "enzyme-linked", but are instead linked to some nonenzymatic reporter.
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Field desorption schematic Field desorption refers to an ion source in which a high-potential electric field is applied to an emitter with a sharp surface, such as a razor blade, or more commonly, a filament from which tiny "whiskers" have formed. This results in a very high electric field which can result in ionization of gaseous molecules of the analyte. Mass spectra produced by FI have little or no fragmentation. They are dominated by molecular radical cations M^{+.
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This process is called Coulombic fission because it is driven by repulsive Coulombic forces between charged molecules. The process repeats until the analyte is free of solvent and is a bare ion. The ions observed are created by the addition of a proton (a hydrogen ion) and denoted [{M}+H]+, or of another cation such as sodium ion, [M + Na]+, or the removal of a proton, [M - H]^-. Multiply charged ions such as [{M}+2H]^2+ are often observed.
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Thermospray ionization has three possible processes by which it can occur. The first involved direct desorption of analyte, where evaporation of the more volatile solvent allows the less volatile liquid sample ions to enter gas phase. The second type of ionization is an acid-base transfer such that solvent ions exchange a proton with ionic components of a buffer. This form of ionization is most commonly used with Reverse phase high performance liquid chromatography (RP-HPLC).
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The laser is fired at the matrix crystals in the dried-droplet spot. The matrix absorbs the laser energy and it is thought that primarily the matrix is desorbed and ionized (by addition of a proton) by this event. The hot plume produced during ablation contains many species: neutral and ionized matrix molecules, protonated and deprotonated matrix molecules, matrix clusters and nanodroplets. Ablated species may participate in the ionization of analyte, though the mechanism of MALDI is still debated.
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Matrix-assisted inlet ionization (MAII) has shown that the laser is not necessary for the ionization process. Ions are formed when matrix-analyte is introduced to the vacuum of a mass spectrometer through an inlet aperture. LSI is a subset of MAII and is now called laserspray inlet ionization (LSII).McEwen C.N.; Pagnotti, V.S.; Inutan, E.D.; Trimpin, S. New Paradigm in Ionization: Multiply Charge Ion Formation from a Solid Matrix without a Laser or Voltage, Anal. Chem.
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ESI-MS was initially developed by Fenn and colleagues for analysis of biomolecules. It depends on the formation of gaseous ions from polar, thermally labile and mostly non- volatile molecules and thus is completely suitable for a variety of lipids. It is a soft-ionization method that rarely disrupts the chemical nature of the analyte prior to mass analysis. Various ESI-MS methods have been developed for analysis of different classes, subclasses, and individual lipid species from biological extracts.
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From an operational standpoint, SFC is as simple and robust as HPLC but fraction collection is more convenient because the primary mobile phase evaporates leaving only the analyte and a small volume of polar co-solvent. If the outlet CO2 is captured, it can be recompressed and recycled, allowing for >90% reuse of CO2. Similar to HPLC, SFC uses a variety of detection methods including UV/VIS, mass spectrometry, FID (unlike HPLC) and evaporative light scattering.
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Any inert polar substance that achieves sufficient packing can be used for reversed-phase chromatography. The most popular column is an octadecyl carbon chain (C18)-bonded silica (USP classification L1). This is followed by C8-bonded silica (L7), pure silica (L3), cyano-bonded silica (L10) and phenyl-bonded silica (L11). Note that C18, C8 and phenyl are dedicated reversed-phase resins, while cyano columns can be used in a reversed-phase mode depending on analyte and mobile phase conditions.
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The gas-phase ions form after the remaining solvent molecules evaporate, leaving the analyte with the charges that the droplet carried. IEM, CRM and CEM schematic. A large body of evidence shows either directly or indirectly that small ions (from small molecules) are liberated into the gas phase through the ion evaporation mechanism, while larger ions (from folded proteins for instance) form by charged residue mechanism. A third model invoking combined charged residue- field emission has been proposed.
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One application of FAIMS is as an additional separation step between the liquid chromatography separation and mass spectrometric analysis in Liquid chromatography–mass spectrometry (LC-MS) as used in proteomic studies. It allows for online fractionation of the analyte components to improve detection of peptides in complex samples. LC-MS uses the mass to charge ratio of peptide ions to analyse samples and the resulting spectra are compared to spectral reference libraries. FAIMS can be used to filter out "chemical noise", i.e.
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Enzymatic methods reduced some interferences but other new ones were discovered. High-performance liquid chromatography, HPLC, was more sensitive and specific, and had become the new reference method endorsed by the American Association for Clinical Chemistry. HPLC addressed the shortcomings of Jaffe-based methods, but was labor- intensive, expensive, and therefore impractical for routine analysis of the most frequently ordered renal analyte in medical labs. Simple, easily automated and cost-effective, Jaffe-based methods have persisted into the 21st century, despite their imperfections.
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Most tests are intended to operate on a purely qualitative basis. However it is possible to measure the intensity of the test line to determine the quantity of analyte in the sample. Handheld diagnostic devices known as lateral flow readers are used by several companies to provide a fully quantitative assay result. By utilizing unique wavelengths of light for illumination in conjunction with either CMOS or CCD detection technology, a signal rich image can be produced of the actual test lines.
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IBBCEAS has been used in conjunction with LEDs and superluminescent LEDs in a number of gas phase and liquid analyte studies. Simultaneous concentration measurements of NO2 and NO3 have been achieved using LED based IBBCEAS within the ppbv detection limit. The advantages of using LEDs as light source are their compactness, long life, power efficiency and price. Also, due to the small area emission, the emitted power per unit area at the peak wavelength can approach that of Xe arc lamps.
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See also Aqueous Normal Phase Chromatography It is commonly believed that in HILIC, the mobile phase forms a water-rich layer on the surface of the polar stationary phase vs. the water-deficient mobile phase, creating a liquid/liquid extraction system. The analyte is distributed between these two layers. However, HILIC is more than just simple partitioning and includes hydrogen donor interactions between neutral polar species as well as weak electrostatic mechanisms under the high organic solvent conditions used for retention.
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One of the industrial uses of TMAH is for the anisotropic etching of silicon. It is used as a basic solvent in the development of acidic photoresist in the photolithography process, and is highly effective in stripping photoresist. TMAH has some phase transfer catalyst properties, and is used as a surfactant in the synthesis of ferrofluid, to inhibit nanoparticle aggregation. TMAH is the most common reagent currently used in thermochemolysis, an analytical technique involving both pyrolysis and chemical derivatization of the analyte.
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In some cases, additional functional groups will need to be added to molecules to facilitate the other separation and analysis methods. Derivatization can change the properties of an analyte; for instance, it would make a polar and non-volatile compound non-polar and more volatile, which would be necessary for analysis in certain types of chromatography. It is important to note, however, that derivatization is not ideal for site-specific analyses as it adds additional elements that must be accounted for in analyses.
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Conductometric sensing involves measuring the change in conductive properties of the sample solution or a medium. The reaction between the biomolecule and analyte changes the ionic species concentration, leading to a change in the solution electrical conductivity or current flow. Two metal electrodes are separated at a certain distance and an AC potential is applied across the electrodes, causing a current flow between the electrodes. During a biorecognition event the ionic composition changes, using an ohmmeter the change in conductance can be measured.
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Illustration of the basic componenets of a CD/DVD based immunoassay, which includes the disk (grey), a probe (green), gold nanoparticle (red), analyte (yellow), and silver particle (blue) A compact disk/digital versatile disk (CD/DVD) based immunoassay is a method for determining the concentration of a compound in research and diagnostic laboratories by performing the test on an adapted CD/DVD surface using an adapted optical disc drive; these methods have been discussed and prototyped in research labs since 1991.
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Initially, analytes in a metabolomic sample comprise a highly complex mixture. This complex mixture can be simplified prior to detection by separating some analytes from others. Separation achieves various goals: analytes which cannot be resolved by the detector may be separated in this step; in MS analysis ion suppression is reduced; the retention time of the analyte serves as information regarding its identity. This separation step is not mandatory and is often omitted in NMR and "shotgun" based approaches such as shotgun lipidomics.
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For analysis by mass spectrometry the analytes must be imparted with a charge and transferred to the gas phase. Electron ionization (EI) is the most common ionization technique applies to GC separations as it is amenable to low pressures. EI also produces fragmentation of the analyte, both providing structural information while increasing the complexity of the data and possibly obscuring the molecular ion. Atmospheric-pressure chemical ionization (APCI) is an atmospheric pressure technique that can be applied to all the above separation techniques.
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TISAB is very commonly applied to fluoride ion analysis such as in fluoride ion selective electrodes. There are four main constituents to TISAB, namely CDTA (cyclohexylenedinitrilotetraacetate), sodium hydroxide, sodium chloride and acetic acid (ethanoic acid), which are all dissolved in deionised water. Hence, TISAB has a density ~1.0 kg/L, though this can vary to 1.18 kg/L. Each constituent plays an important role in controlling the ionic strength and pH of the analyte solution, which may otherwise cause error and inaccuracy.
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Each instrument used in analytical chemistry has a useful working range. This is the range of concentration (or mass) that can be adequately determined by the instrument, where the instrument provides a useful signal that can be related to the concentration of the analyte. All instruments have an upper and a lower working limit. Concentrations below the working limit do not provide enough signal to be useful, and concentrations above the working limit provide too much signal to be useful.
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Under these conditions, about 1 in 1000 analyte molecules in the source are ionized. At higher energies, the de Broglie wavelength of the electrons becomes smaller than the bond lengths in typical analytes; the molecules then become "transparent" to the electrons and ionization efficiency decreases. The effective ionizing path length (L) can be increased by using a weak magnetic field. But the most practical way to increase the sample current is to operate the ion source at higher ionizing current (Ie).
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Originally based near Detroit, Michigan, and founded by Charles McGrath in 1986, Grace Bio Labs relocated to Bend, Oregon in May, 1990. With the aid of SBIR funding, Grace Bio-Labs was built on two main product types. The first is the incubation chamber for cell culture and analysis; the second is the ONCYTE Nitrocellulose Film Slide. Their incubation and hybridization chambers are fluid delivery and containment products that increase sensitivity and efficiency in fluorescence and color- based protein and cell analyte assays.
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Sometimes two different molecules can also have a similar pattern of ionized fragments in a mass spectrometer (mass spectrum). Combining the two processes reduces the possibility of error, as it is extremely unlikely that two different molecules will behave in the same way in both a gas chromatograph and a mass spectrometer. Therefore, when an identifying mass spectrum appears at a characteristic retention time in a GC-MS analysis, it typically increases certainty that the analyte of interest is in the sample.
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Ingestion of codeine or food containing poppy seeds can cause false positives. A 1999 review estimated that relatively low doses of heroin (which metabolizes immediately into morphine) are detectable by standard urine tests for 1–1.5 days after use. A 2009 review determined that, when the analyte is morphine and the limit of detection is 1ng/ml, a 20mg intravenous (IV) dose of morphine is detectable for 12–24 hours. A limit of detection of 0.6ng/ml had similar results.
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In analytical chemistry, sample preparation refers to the ways in which a sample is treated prior to its analyses. Preparation is a very important step in most analytical techniques, because the techniques are often not responsive to the analyte in its in-situ form, or the results are distorted by interfering species. Sample preparation may involve dissolution, extraction, reaction with some chemical species, pulverizing, treatment with a chelating agent (e.g. EDTA), masking, filtering, dilution, sub-sampling or many other techniques.
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The APPI interface for LC-MS was developed simultaneously by Bruins and Syage in 2000. APPI is another LC-MS ion source/ interface for the analysis of neutral compounds that cannot be ionized using ESI. This interface is similar to the APCI ion source, but instead of a corona discharge, the ionization occurs by using photons coming from a discharge lamp. In the direct-APPI mode, singly charged analyte molecular ions are formed by absorption of a photon and ejection of an electron.
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GC-VUV can be used for bulk compositional analysis because compounds share spectral shape characteristics within a class. Proprietary software applies fitting procedures to quickly determine the relative contribution of each compound category present in a sample. Retention index information is used to limit the amount of VUV library searching and fitting performed for each analyte, enabling the automated data processing routine to be completed quickly. Compound class or specific compound concentrations can be reported as either mass or volume percent.
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As a separation technique, GPC has many advantages. First of all, it has a well-defined separation time due to the fact that there is a final elution volume for all unretained analytes. Additionally, GPC can provide narrow bands, although this aspect of GPC is more difficult for polymer samples that have broad ranges of molecular weights present. Finally, since the analytes do not interact chemically or physically with the column, there is a lower chance for analyte loss to occur.
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Isotope dilution is almost exclusively employed with mass spectrometry in applications where high-accuracy is demanded. For example, all National Metrology Institutes rely significantly on isotope dilution when producing certified reference materials. In addition to high-precision analysis, isotope dilution is applied when low recovery of the analyte is encountered. In addition to the use of stable isotopes, radioactive isotopes can be employed in isotope dilution which is often encountered in biomedical applications, for example, in estimating the volume of blood.
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The retention time measured under particular conditions is an identifying characteristic of a given analyte. Many different types of columns are available, filled with adsorbents varying in particle size, and in the nature of their surface ("surface chemistry"). The use of smaller particle size packing materials requires the use of higher operational pressure ("backpressure") and typically improves chromatographic resolution (the degree of peak separation between consecutive analytes emerging from the column). Sorbent particles may be hydrophobic or polar in nature.
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A popular form of ITP is transient ITP (tITP). It alleviates the limitation of conventional ITP that it has limited separation capacity because of analyte zone overlap. In transient ITP, analytes are first concentrated by ITP, and then can be baseline separated by zone electrophoresis. Transient ITP is usually accomplished by dissolving the sample in the TE and sandwiching the sample/TE plug between LE zones - or vice versa: a sample/LE plug can also be sandwiched between TE zones.
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PDB record 1KBH The analyte molecules in a sample can be partially ordered with respect to the external magnetic field of the spectrometer by manipulating the sample conditions. Common techniques include addition of bacteriophages or bicelles to the sample, or preparation of the sample in a stretched polyacrylamide gel. This creates a local environment that favours certain orientations of nonspherical molecules. Normally in solution NMR the dipolar couplings between nuclei are averaged out because of the fast tumbling of the molecule.
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Gas phase titrations are titrations done in the gas phase, specifically as methods for determining reactive species by reaction with an excess of some other gas, acting as the titrant. In one common gas phase titration, gaseous ozone is titrated with nitrogen oxide according to the reaction :O3 \+ NO → O2 \+ NO2. After the reaction is complete, the remaining titrant and product are quantified (e.g., by Fourier transform spectroscopy) (FT-IR); this is used to determine the amount of analyte in the original sample.
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Different types of mass analyzers, ToF, qudrupole, etc., can be used in the MS. Common solvents used in normal or reversed phase LC such as water, acetonitrile, and methanol are all compatible with ESI, yet a LC grade solvent may not be suitable for MS. Furthermore, buffers containing inorganic ions should be avoided as they may contaminate the ion source. Nonetheless, the problem can be resolved by 2D LC- MS, as well as other various issues including analyte coelusion and UV detection responses.
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Alena Bulyha, Clemens Heitzinger and Norbert J Mauser: Bio-Sensors: Modelling and Simulation of Biologically Sensitive Field-Effect- Transistors, ERCIM News, 04,2011. Once the analyte binds to the recognition element, the charge distribution at the surface changes with a corresponding change in the electrostatic surface potential of the semiconductor. This change in the surface potential of the semiconductor acts like a gate voltage would in a traditional MOSFET, i.e. changing the amount of current that can flow between the source and drain electrodes.
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The eluent is optimized in small scale pretests, often using thin layer chromatography (TLC) with the same stationary phase. There is an optimum flow rate for each particular separation. A faster flow rate of the eluent minimizes the time required to run a column and thereby minimizes diffusion, resulting in a better separation. However, the maximum flow rate is limited because a finite time is required for the analyte to equilibrate between the stationary phase and mobile phase, see Van Deemter's equation.
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This isolates the undesired redox events taking place at the auxiliary electrode. During bulk electrolysis, the analyte undergoes a redox event at the working electrode. If the system was open, then it would be possible for the product of that reaction to diffuse back to the auxiliary electrode and undergo the inverse redox reaction. In addition to maintaining the proper current at the working electrode, the auxiliary electrode will experience extreme potentials often oxidizing or reducing the solvent or electrolyte to balance the current.
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In mass spectrometry, direct analysis in real time (DART) is an ion source that produces electronically or vibronically excited-state species from gases such as helium, argon, or nitrogen that ionize atmospheric molecules or dopant molecules. The ions generated from atmospheric or dopant molecules undergo ion-molecule reactions with the sample molecules to produce analyte ions. Analytes with low ionization energy may be ionized directly. The DART ionization process can produce positive or negative ions depending on the potential applied to the exit electrode.
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An example of a recently developed biosensor is one for detecting cytosolic concentration of the analyte cAMP (cyclic adenosine monophosphate), a second messenger involved in cellular signaling triggered by ligands interacting with receptors on the cell membrane. Similar systems have been created to study cellular responses to native ligands or xenobiotics (toxins or small molecule inhibitors). Such "assays" are commonly used in drug discovery development by pharmaceutical and biotechnology companies. Most cAMP assays in current use require lysis of the cells prior to measurement of cAMP.
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It is a useful matrix for a wide variety of peptides and proteins. It serves well as a matrix for MALDI due to its ability to absorb laser radiation and to also donate protons (H+) to the analyte of interest. Sinapic acid can form dimers with itself (one structure) and ferulic acid (three different structures) in cereal cell walls and therefore may have a similar influence on cell-wall structure to that of the diferulic acids. Sinapine is an alkaloidal amine found in black mustard seeds.
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Dilution of sample or reducing the volume of sample injected may give a reduction of ion suppression by reducing the quantity of interfering species present, although the quantity of analyte of interest will also be reduced, making this an undesirable approach for trace analysis. Similar is the effect of reducing the mobile phase flow rate to the nanolitre- per-minute range since, in addition to resulting in improved desolvation, the smaller droplets formed are more tolerant to the presence of non-volatile species in the sample matrix.
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For matrix matched calibration standards to be effective in compensating for ion suppression, the sample matrix must be free of the analyte of interest. Additionally, it is important that there is little variation in test sample composition since both the test sample and the prepared calibration sample must be affected in the same way by ion suppression. Again, in complex biological samples from different individuals, or even the same individual at a different time, there may be large fluctuations in the concentrations of ion suppressing species.
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338x338pxAn illustration of the MSIA procedure is depicted in the figure to the right. Analytes in a biological liquid sample are collected from solution by using a MSIA tip (also known as MSIA microcolumns) that contains a derivatized affinity frit. Biological samples contain various proteins that span a wide dynamic range so purification is needed to minimize the complex matrix and maximize mass spectrometry sensitivity. the MSIA tip serves as a place to purify these samples by immobilizing the analyte with high selectivity and specificity.
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The effect can also occur because of antigen excess, when both the capture and detection antibodies become saturated by the high analyte concentration. In this case, no sandwich can be formed by the capturing antibody, the antigen and the detection antibody. In this case, free antigen is in competition with captured antigen for detection antibody binding. Sequential addition of antigen and antibody, paired with stringent washing, can prevent the effect, as can increasing the relative concentration of antibody to antigen, thereby mediating the effect.
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In order to make conclusions about relative intensity a great deal of knowledge and care is required. A common way to get more quantitative information out of a mass spectrum is to create a standard curve to compare the sample to. This requires knowing what is to be quantitated ahead of time, having a standard available and designing the experiment specifically for this purpose. A more advanced variation on this is the use of an internal standard which behaves very similarly to the analyte.
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In DESI, there is a high-velocity pneumatically assisted electrospray jet that is continually directed towards the probe surface. The jet forms a micrometer-size thin solvent film on the sample where it can be desorbed. The sample can be dislodged by the incoming spray jet allowing for particles to come off in an ejection cone of analyte containing secondary ion droplets. A lot of study is still going into looking at the working principals of DESI but there are still some things known.
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The chip with crystallized analyte is then placed in to the MALDI-MS for analysis. One issue raised with MALDI-MS coupling to DMF is that the matrix necessary for MALDI-MS can be highly acidic, which may interfere with the on-chip reactions Inline analysis is the usage of devices that feed directly into mass spectrometers, thereby eliminating any manual manipulation. Inline analysis may require specially fabricated devices and connecting hardware between the device and the mass spectrometer. Inline analysis is often coupled with electrospray ionization.
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An Electrospray ionization (ESI) source is located above the sample for post-ablation ionization. The jet of ablated material is intersected and ionized by a spray plume from the ESI source located above the sample. The ionized molecules are then swept into the mass spectrometer for analysis. Because an ESI source is used for ionization, the LAESI mass spectra are similar to traditional ESI spectra, which can exhibit multiply charged analyte peaks, and extend the effective mass range of detection to biomolecules >100,000 Da in size.
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A typical titration curve of a diprotic acid titrated with a strong base. Shown here is oxalic acid titrated with sodium hydroxide. Both equivalence points are visible. A titration curve is a curve in graph the x-coordinate of which represents the volume of titrant added since the beginning of the titration, and the y-coordinate of which represents the concentration of the analyte at the corresponding stage of the titration (in an acid–base titration, the y-coordinate usually represents the pH of the solution).
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This mode is specialized for analyzing liquid samples, with a metal or polymer mesh replacing the sample plate in reflection geometry. The mesh is oriented 180^\circ from the nebulizer microchip and the mass spec inlet, with the lamp directing photons to the area where the mesh releases newly desorbed molecules. The analyte is thermally desorbed as both the dopant vapor and nebulizer gas are directed through the mesh. It has been seen that steel mesh with low density and narrow strands produces better signal intensities.
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Peptide microarrays can be used to study different kinds of protein-protein interactions, specially those involving modular protein substructures called peptide recognition modules or, most commonly, protein interaction domains. The reason for this is that such protein substructures recognize short linear motifs often exposed in natively unstructured regions of the binding partner, such that the interaction can be modelled in vitro by peptides as probes and the peptide recognition module as analyte. Most publications can be found in the context of immune monitoring and enzyme profiling.
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Chemical ionization for gas phase analysis is either positive or negative. Almost all neutral analytes can form positive ions through the reactions described above. In order to see a response by negative chemical ionization (NCI, also NICI), the analyte must be capable of producing a negative ion (stabilize a negative charge) for example by electron capture ionization. Because not all analytes can do this, using NCI provides a certain degree of selectivity that is not available with other, more universal ionization techniques (EI, PCI).
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This top-down fabrication technique allows the fabrication of a large variety of SiNWs with different shapes, from angular to circular. It also allows the precise positioning of the silicon nanowires in ant desired position, making easier its integration; indeed, this technique is compatible with the standard silicon CMOS processing technology. Single crystalline silicon nanowires have already shown a great potential as ultrasensitive sensors by detecting changes in the nanowire conductivity when a specific analyte is present. Local oxidation nanolithography, therefore, is a promising technique to allow the realisation of array of biosensors.
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John Fenn's Nobel Prize winning work on electrospray ionization Field desorption ionization was first reported by Beckey in 1969. In field ionization, a high-potential electric field is applied to an emitter with a sharp surface, such as a razor blade, or more commonly, a filament from which tiny "whiskers" have been grown. This produces a very high electric field in which electron tunneling can result in ionization of gaseous analyte molecules. FI produces mass spectra with little or no fragmentation, dominated by molecular radical cations M+. and occasionally protonated molecules [M+H]^+.
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The first quadrupole mass filter, Q1, is the primary m/z selector after the sample leaves the ionization source. Any ions with mass-to-charge ratios other than the one selected for will not be allowed to infiltrate Q1. The collision cell, denoted as "q", is located between Q1 and Q3, is where fragmentation of the sample occurs in the presence of an inert gas like Ar, He, or N2. A characteristic daughter ion is produced as a result of the collisions of the inert gas with the analyte.
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Using image processing algorithms specifically designed for a particular test type and medium, line intensities can then be correlated with analyte concentrations. One such handheld lateral flow device platform is made by Detekt Biomedical L.L.C.. Alternative non-optical techniques are also able to report quantitative assays results. One such example is a magnetic immunoassay (MIA) in the lateral flow test form also allows for getting a quantified result. Reducing variations in the capillary pumping of the sample fluid is another approach to move from qualitative to quantitative results.
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Nuclease hybridization assay The nuclease hybridization assay, also called S1 nuclease cutting assay, is a nuclease protection assay-based hybridization ELISA. The assay is using S1 nuclease, which degrades single-stranded DNA and RNA into oligo- or mononucleotides, leaving intact double-stranded DNA and RNA. In the nuclease hybridization assay, the oligonucleotide analyte is captured onto the solid support such as a 96-well plate via a fully complementary cutting probe. After enzymatic processing by S1 nuclease, the free cutting probe and the cutting probe hybridized to metabolites, i.e.
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Liver cell glycogen can be converted to glucose and returned to the blood when insulin is low or absent; muscle cell glycogen is not returned to the blood because of a lack of enzymes. In fat cells, glucose is used to power reactions that synthesize some fat types and have other purposes. Glycogen is the body's "glucose energy storage" mechanism, because it is much more "space efficient" and less reactive than glucose itself. As a result of its importance in human health, glucose is an analyte in glucose tests that are common medical blood tests.
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A three-dimensional structure of the "sex hormone-binding globulin (SHBG)". One often cited criticism of using saliva as a diagnostic fluid is that biomarkers are present in amounts that are too low to be detected reliably. As Wong points out, however, this “is no longer a limitation” due to the development of increasingly sensitive detection techniques. Advances in ELISA and mass spectrometry, in addition to the emergence of novel detection methods that take advantage of nanotechnology and other technologies, are enabling scientists and practitioners to achieve high analyte sensitivity.
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Compiled data sets include a variety of endpoints including mortality, reproduction, growth rate, and juvenile survival in sediment toxicity data sets for all organisms for which tests have been conducted. Studies are screened, and only those assays using standardized methods and resulting in significant effects are used for the determination of ERL/ERM guidelines. In summary, the key links between the compiled studies are the testing of a specific analyte - toxicity assays used are for sediment, and a significant effect must be determined. The data is arranged by ordering the concentrations from lowest to highest.
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Solid-phase microextraction (SPME), is a solid phase extraction technique that involves the use of a fiber coated with an extracting phase, that can be a liquid (polymer) or a solid (sorbent), which extracts different kinds of analytes (including both volatile and non- volatile) from different kinds of media, that can be in liquid or gas phase. The quantity of analyte extracted by the fibre is proportional to its concentration in the sample as long as equilibrium is reached or, in case of short time pre-equilibrium, with help of convection or agitation.
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In electrochemistry, the diffusion layer, according to IUPAC, is defined as the "region in the vicinity of an electrode where the concentrations are different from their value in the bulk solution. The definition of the thickness of the diffusion layer is arbitrary because the concentration approaches asymptotically the value in the bulk solution". The diffusion layer thus depends on the diffusion coefficient (D) of the analyte and for voltammetric measurements on the scan rate (V/s). It is usually considered to be some multiple of (Dt)1/2 (where 1/t = scan rate).
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1988 The parameters that are measured are referred to as the glass transition value (Tg) and melting temperature (Tm). These values are measured over time and are comparable between an inert reference sample and the analyte. Changes in the (Tm) and (Tg) values evaluate phase changes (solid, liquid-gel, liquid, etc.) in which an endothermic or exothermic process occurs. This technique is useful for monitoring the phase changes in phospholipids by providing information such as the amount of heat released or absorbed and time for phase transitions to occur, etc.
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A testing dipstick is usually made of paper or cardboard and is impregnated with reagents that indicate some feature of the liquid by changing color. In medicine, dipsticks can be used to test for a variety of liquids for the presence of a given substance, known as an analyte. For example, urine dipsticks are used to test urine samples for haemoglobin, nitrite (produced by bacteria in a urinary tract infection), protein, nitrocellulose, glucose and occasionally urobilinogen or ketones. They are usually brightly coloured, and extremely rough to the touch.
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In the case of non- volatile target analytes, the presence of the keeper solvent or solid is intended to prevent all the solvent from being evaporated off, thereby preventing the loss of analytes which might irreversibly adsorb to the container walls when completely dried, or if it is totally dried (in the case of a solid keeper), provide a surface where the analyte can be reversibly rather than irreversibly adsorbed A solid keeper of sodium sulfate was effective for reducing losses of polycyclic aromatic hydrocarbons (PAHs) in an evaporative procedure.
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Mechanism of capillary electrochromatography Capillary electrochromatography (CEC) is a chromatographic technique in which the mobile phase is driven through the chromatographic bed by electroosmosis. Capillary electrochromatography is a combination of two analytical techniques, high- performance liquid chromatography and capillary electrophoresis. Capillary electrophoresis aims to separate analytes on the basis of their mass-to-charge ratio by passing a high voltage across ends of a capillary tube, which is filled with the analyte. High-performance liquid chromatography separates analytes by passing them, under high pressure, through a column filled with stationary phase.
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The radioactive foil emits a beta particle (electron) which collides with and ionizes the carrier gas to generate more ions resulting in a current. When analyte molecules with electronegative / withdrawing elements or functional groups electrons are captured which results in a decrease in current generating a detector response. Nitrogen–phosphorus detector (NPD), a form of thermionic detector where nitrogen and phosphorus alter the work function on a specially coated bead and a resulting current is measured. Dry electrolytic conductivity detector (DELCD) uses an air phase and high temperature (v.
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In mass spectrometry, liquid junction interface is an ion source or set-up that couples peripheric devices, such as capillary electrophoresis, to mass spectrometry. See the IUPAC recommendation definition as a means of coupling capillary electrophoresis to mass spectrometry in which a liquid reservoir surrounds the separation capillary and transfer capillary to the mass spectrometer. The reservoir provides electrical contact for the capillary electrophoresis. The term liquid junction interface has also been used by Henry M. Fales and coworkers for ion sources where the analyte is in direct contact with the high voltage supply.
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On the other hand, soft ionization techniques such as ESI are, in some cases, far more efficient but generate fewer fragment ions. The cost of this attitude is paid in terms of structural information so that a second analyzer to generate MS/MS spectra is an obligation. A typical EI spectrum, in general, has extensive structural information, and a cheaper, single-stage mass spectrometer might be sufficient for analyte characterization or identification. As a rule of the thumb, nanogram-level sensitivity is obtained in full-scan mode for most substances.
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Unlike in linear sweep voltammetry, after the set potential is reached in a CV experiment, the working electrode's potential is ramped in the opposite direction to return to the initial potential. These cycles of ramps in potential may be repeated as many times as needed. The current at the working electrode is plotted versus the applied voltage (that is, the working electrode's potential) to give the cyclic voltammogram trace. Cyclic voltammetry is generally used to study the electrochemical properties of an analyte in solution or of a molecule that is adsorbed onto the electrode.
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Undergraduate Instrumental Analysis, 6th ed. Marcel Drekker, New York, 2005 The fragmentation in electron ionization can be described using Born Oppenheimer potential curves as in the diagram. The red arrow shows the electron impact energy which is enough to remove an electron from the analyte and form a molecular ion from non- dissociative results. Due to the higher energy supplied by 70 eV electrons other than the molecular ion, several other bond dissociation reactions can be seen as dissociative results, shown by the blue arrow in the diagram.
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Less volatile matrices such as 2,5-dihydroxybenzoic acid require a hot inlet tube to produce analyte ions by MAI, but more volatile matrices such as 3-nitrobenzonitrile require no heat, voltage, or laser. Simply introducing the matrix:analyte sample to the inlet aperture of an atmospheric pressure ionization mass spectrometer produces abundant ions. Compounds at least as large as bovine serum albumin [66 kDa] can be ionized with this method. In this simple, low cost and easy to use ionization method, the inlet to the mass spectrometer can be considered the ion source.
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Because like charges repel, the liquid pushes itself out of the capillary and forms an aerosol, a mist of small droplets about 10 μm across. The aerosol is at least partially produced by a process involving the formation of a Taylor cone and a jet from the tip of this cone. An uncharged carrier gas such as nitrogen is sometimes used to help nebulize the liquid and to help evaporate the neutral solvent in the droplets. As the solvent evaporates, the analyte molecules are forced closer together, repel each other and break up the droplets.
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Hydrodynamic voltammetry is a form of voltammetry in which the analyte solution flows relative to a working electrode. In many voltammetry techniques, the solution is intentionally left still to allow diffusion controlled mass transfer. When a solution is made to flow, through stirring or some other physical mechanism, it is very important to the technique to achieve a very controlled flux or mass transfer in order to obtain predictable results. These methods are types of electrochemical studies which use potentiostats to investigate reaction mechanisms related to redox chemistry among other chemical phenomenon.
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The reaction is: Formation of calcium oxalate: Ca2+(aq) \+ C2O42- → CaC2O4 The precipitate is collected, dried and ignited to high (red) heat which converts it entirely to calcium oxide. The reaction is pure calcium oxide formed CaC2O4 → CaO(s) \+ CO(g)\+ CO2(g) The pure precipitate is cooled, then measured by weighing, and the difference in weights before and after reveals the mass of analyte lost, in this case calcium oxide. That number can then be used to calculate the amount, or the percent concentration, of it in the original mix.
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In ET AAS a transient signal is generated, the area of which is directly proportional to the mass of analyte (not its concentration) introduced into the graphite tube. This technique has the advantage that any kind of sample, solid, liquid or gaseous, can be analyzed directly. Its sensitivity is 2–3 orders of magnitude higher than that of flame AAS, so that determinations in the low μg L−1 range (for a typical sample volume of 20 μL) and ng g−1 range (for a typical sample mass of 1 mg) can be carried out.
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Electrodeless discharge lamps (EDL) contain a small quantity of the analyte as a metal or a salt in a quartz bulb together with an inert gas, typically argon gas, at low pressure. The bulb is inserted into a coil that is generating an electromagnetic radio frequency field, resulting in a low-pressure inductively coupled discharge in the lamp. The emission from an EDL is higher than that from an HCL, and the line width is generally narrower, but EDLs need a separate power supply and might need a longer time to stabilize.
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Another source of background absorption, particularly in ET AAS, is scattering of the primary radiation at particles that are generated in the atomization stage, when the matrix could not be removed sufficiently in the pyrolysis stage. All these phenomena, molecular absorption and radiation scattering, can result in artificially high absorption and an improperly high (erroneous) calculation for the concentration or mass of the analyte in the sample. There are several techniques available to correct for background absorption, and they are significantly different for LS AAS and HR-CS AAS.
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Mass spectrometric immunoassay (MSIA) is a rapid method is used to detect and/ or quantify antigens and or antibody analytes. This method uses an analyte affinity (either through antigens or antibodies) isolation to extract targeted molecules and internal standards from biological fluid in preparation for matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS). This method allows for "top down" and "bottom up" analysis. This sensitive method allows for a new and improved process for detecting multiple antigens and antibodies in a single assay.
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In chromatography, the retardation factor (R) is the fraction of an analyte in the mobile phase of a chromatographic system. In planar chromatography in particular, the retardation factor Rf is defined as the ratio of the distance traveled by the center of a spot to the distance traveled by the solvent front. Ideally, the values for RF are equivalent to the R values used in column chromatography. Although the term retention factor is sometimes used synonymously with retardation factor in regard to planar chromatography the term is not defined in this context.
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Iodometry, known as iodometric titration, is a method of volumetric chemical analysis, a redox titration where the appearance or disappearance of elementary iodine indicates the end point. Note that iodometry involves indirect titration of iodine liberated by reaction with the analyte, whereas iodimetry involves direct titration using iodine as the titrant. Redox titration using sodium thiosulphate, Na2S2O3 (usually) as a reducing agent is known as iodometric titration since it is used specifically to titrate iodine. The iodometric titration is a general method to determine the concentration of an oxidising agent in solution.
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Magnetic immunoassay (MIA) is a novel type of diagnostic immunoassay utilizing magnetic nanobeads as labels in lieu of conventional, enzymes, radioisotopes or fluorescent moieties. This assay involves the specific binding of an antibody to its antigen, where a magnetic label is conjugated to one element of the pair. The presence of magnetic nanobeads is then detected by a magnetic reader (magnetometer) which measures the magnetic field change induced by the beads. The signal measured by the magnetometer is proportional to the analyte (virus, toxin, bacteria, cardiac marker, etc.) quantity in the initial sample.
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The sample is continuously irradiated with a beam of neutrons. The constituent elements of the sample absorb some of these neutrons and emit prompt gamma rays which are measured with a gamma ray spectrometer. The energies of these gamma rays identify the neutron-capturing elements, while the intensities of the peaks at these energies reveal their concentrations. The amount of analyte element is given by the ratio of count rate of the characteristic peak in the sample to the rate in a known mass of the appropriate elemental standard irradiated under the same conditions.
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A chromatography detector is a device used in gas chromatography (GC) or liquid chromatography (LC) to detect components of the mixture being eluted off the chromatography column. There are two general types of detectors: destructive and non-destructive. The destructive detectors perform continuous transformation of the column effluent (burning, evaporation or mixing with reagents) with subsequent measurement of some physical property of the resulting material (plasma, aerosol or reaction mixture). The non-destructive detectors are directly measuring some property of the column eluent (for example UV absorption) and thus affords greater analyte recovery.
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This makes it necessary to dilute aqueous samples into the dynamic range of the specific analyte. GFAAS with automatic software can also pre-dilute samples before analysis. After the instrument has warmed up and been calibrated, a small aliquot (usually less than 100 microliters (µL) and typically 20 µL) is placed, either manually or through an automated sampler, into the opening in the graphite tube. The sample is vaporized in the heated graphite tube; the amount of light energy absorbed in the vapor is proportional to atomic concentrations.
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The relative contribution of each analyte is shown relative to the sum absorbance. The flow rate-enhanced chromatographic compression strategy has been applied to a diverse set of applications since the development of the GC-VUV method for residual solvents analysis. The fast GC-VUV approach reduced GC runtimes for terpene analysis from 30 minutes to 9 minutes (the deconvolution of monoterpene isomers is shown in Figure 4). It has also been demonstrated that GC runtimes as short as 14 minutes can be used for PIONA compound analysis of gasoline samples.
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Mixing of the isotopic standard with the sample effectively "dilutes" the isotopic enrichment of the standard and this forms the basis for the isotope dilution method. Isotope dilution is classified as a method of internal standardisation, because the standard (isotopically-enriched form of analyte) is added directly to the sample. In addition, unlike traditional analytical methods which rely on signal intensity, isotope dilution employs signal ratios. Owing to both of these advantages, the method of isotope dilution is regarded among chemistry measurement methods of the highest metrological standing.
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Normal–phase chromatography was one of the first kinds of HPLC that chemists developed. Also known as normal-phase HPLC (NP-HPLC) this method separates analytes based on their affinity for a polar stationary surface such as silica, hence it is based on analyte ability to engage in polar interactions (such as hydrogen-bonding or dipole-dipole type of interactions) with the sorbent surface. NP-HPLC uses a non-polar, non-aqueous mobile phase (e.g., Chloroform), and works effectively for separating analytes readily soluble in non-polar solvents.
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Branched chain compounds elute more rapidly than their corresponding linear isomers because the overall surface area is decreased. Similarly organic compounds with single C–C bonds elute later than those with a C=C or C–C triple bond, as the double or triple bond is shorter than a single C–C bond. Aside from mobile phase surface tension (organizational strength in eluent structure), other mobile phase modifiers can affect analyte retention. For example, the addition of inorganic salts causes a moderate linear increase in the surface tension of aqueous solutions (ca.
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Isocratic elution is typically effective in the separation of sample components that are very different in their affinity for the stationary phase. In gradient elution the composition of the mobile phase is varied typically from low to high eluting strength. The eluting strength of the mobile phase is reflected by analyte retention times with high eluting strength producing fast elution (=short retention times). A typical gradient profile in reversed phase chromatography might start at 5% acetonitrile (in water or aqueous buffer) and progress linearly to 95% acetonitrile over 5–25 minutes.
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Surface plasmon resonance (SPR) is the most common label-free technique for the measurement of biomolecular interactions. SPR instruments measure the change in the refractive index of light reflected from a metal surface (the "biosensor"). Binding of biomolecules to the other side of this surface leads to a change in the refractive index which is proportional to the mass added to the sensor surface. In a typical application, one binding partner (the "ligand", often a protein) is immobilized on the biosensor and a solution with potential binding partners (the "analyte") is channelled over this surface.
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Though the terms equivalence point and endpoint are often used interchangeably, they are different terms. Equivalence point is the theoretical completion of the reaction: the volume of added titrant at which the number of moles of titrant is equal to the number of moles of analyte, or some multiple thereof (as in polyprotic acids). Endpoint is what is actually measured, a physical change in the solution as determined by an indicator or an instrument mentioned above. There is a slight difference between the endpoint and the equivalence point of the titration.
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Wilm and Mann demonstrated that a capillary flow of ~ 25 nL/min can sustain an electrospray at the tip of emitters fabricated by pulling glass capillaries to a few micrometers. The latter was renamed nano-electrospray (nanospray) in 1996. Currently the name nanospray is also in use for electrosprays fed by pumps at low flow rates, not only for self-fed electrosprays. Although there may not be a well-defined flow rate range for electrospray, microspray, and nano- electrospray, studied "changes in analyte partition during droplet fission prior to ion release".
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Immunoassays rely on the ability of an antibody to recognize and bind a specific macromolecule in what might be a complex mixture of macromolecules. In immunology the particular macromolecule bound by an antibody is referred to as an antigen and the area on an antigen to which the antibody binds is called an epitope. In some cases, an immunoassay may use an antigen to detect for the presence of antibodies, which recognize that antigen, in a solution. In other words, in some immunoassays, the analyte may be an antibody rather than an antigen.
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Concurrently, the neutral analyte molecules of a sample vapor enter the flow tube, via a heated sampling tube, where they meet the precursor ions and may undergo chemical ionization, depending on their chemical properties, such as their proton affinity or ionization energy. The newly formed "product ions" flow into the mass spectrometer chamber, which contains a second quadrupole mass filter, and an electron multiplier detector, which are used to separate the ions by their mass-to-charge ratios (m/z) and measure the count rates of the ions in the desired m/z range.
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In proton NMR spectroscopy, deuterated solvent (enriched to >99% deuterium) must be used to avoid recording a large interfering signal or signals from the proton(s) (i.e., hydrogen-1) present in the solvent itself. If nondeuterated chloroform (containing a full equivalent of protium) were used as solvent, the solvent signal would almost certainly overwhelm and obscure any nearby analyte signals. In addition, modern instruments usually require the presence of deuterated solvent, as the field frequency is locked using the deuterium signal of the solvent to prevent frequency drift.
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The advantages of fluorescence emission being 'switched on' from 'off' upon the recognition event enabling the chemosensors to be compared to 'beacons in the night'. As the process is reversible, the emission enhancement is concentration dependent, only becoming 'saturated' at high concentrations (fully bound receptor). Hence, a correlation can be made between luminescence (intensity, quantum yield and in some cases lifetime) and the analyte concentration. Through careful design, and evaluation of the nature of the communication pathway, similar sensors based on the use of 'on-off' switching, or 'on-off-on,' or 'off-on-off' switching have been designed.
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Schematic of SAII Solvent assisted inlet ionization (SAII) is similar to matrix-assisted inlet ionization however the matrix is a solvent such as water, acetonitrile and methanol. This ionization technique is highly sensitive to small molecules, peptides and proteins. The analyte is dissolved in the solvent and can either be introduced to the heated inlet tube by a capillary column or directly injected into the inlet tube with a syringe or by pipetting. The capillary column is made of fused silica particles with one end submerged in the sample solvent and the other in the end of the heated inlet tube.
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The first SPR immunoassay was proposed in 1983 by Liedberg, Nylander, and Lundström, then of the Linköping Institute of Technology (Sweden). They adsorbed human IgG onto a 600-angstrom silver film, and used the assay to detect anti-human IgG in water solution. Unlike many other immunoassays, such as ELISA, an SPR immunoassay is label free in that a label molecule is not required for detection of the analyte. Additionally, the measurements on SPR can be followed real-time allowing the monitoring of individual steps in sequential binding events particularly useful in the assessment of for instance sandwich complexes.
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The recently developed liquid injection FD ionization (LIFDI) technique "presents a major breakthrough for FD-MS of reactive analytes": Transition metal complexes are neutral and due to their reactivity, do not undergo protonation or ion attachment. They benefit from both: the soft FD ionization and the safe and simple LIFDI transfer of air/moisture sensitive analyte solution. This transfer occurs from the Schlenk flask to the FD emitter in the ion source through a fused silica capillary without breaking the vacuum. LIFDI has been successfully coupled to a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer.
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The types of gel most typically used are agarose and polyacrylamide gels. Each type of gel is well-suited to different types and sizes of the analyte. Polyacrylamide gels are usually used for proteins and have very high resolving power for small fragments of DNA (5-500 bp). Agarose gels, on the other hand, have lower resolving power for DNA but have a greater range of separation, and are therefore used for DNA fragments of usually 50–20,000 bp in size, but the resolution of over 6 Mb is possible with pulsed field gel electrophoresis (PFGE).
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Both types of column are made from non- adsorbent and chemically inert materials. Stainless steel and glass are the usual materials for packed columns and quartz or fused silica for capillary columns. Gas chromatography is based on a partition equilibrium of analyte between a solid or viscous liquid stationary phase (often a liquid silicone- based material) and a mobile gas (most often helium). The stationary phase is adhered to the inside of a small-diameter (commonly 0.53 – 0.18mm inside diameter) glass or fused-silica tube (a capillary column) or a solid matrix inside a larger metal tube (a packed column).
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Solid-phase microextraction sampling Solid phase microextraction, or SPME, is a solid phase extraction sampling technique that involves the use of a fiber coated with an extracting phase, that can be a liquid (polymer) or a solid (sorbent), which extracts different kinds of analytes (including both volatile and non-volatile) from different kinds of media, that can be in liquid or gas phase. The quantity of analyte extracted by the fibre is proportional to its concentration in the sample as long as equilibrium is reached or, in case of short time pre-equilibrium, with help of convection or agitation.
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Each data set contains a veritable gallery of pictures because any peak in each spectrum can be spatially mapped. Despite the fact that MSI has been generally considered a qualitative method, the signal generated by this technique is proportional to the relative abundance of the analyte. Therefore, quantification is possible, when its challenges are overcome. Although widely used traditional methodologies like radiochemistry and immunohistochemistry achieve the same goal as MSI, they are limited in their abilities to analyze multiple samples at once, and can prove to be lacking if researchers do not have prior knowledge of the samples being studied.
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Developments within SIMS: Some chemical modifications have been made within SIMS to increase the efficiency of the process. There are currently two separate techniques being used to help increase the overall efficiency by increasing the sensitivity of SIMS measurements: matrix-enhanced SIMS (ME-SIMS) - This has the same sample preparation as MALDI does as this simulates the chemical ionization properties of MALDI. ME-SIMS does not sample nearly as much material. However, if the analyte being tested has a low mass value then it can produce a similar looking spectra to that of a MALDI spectra.
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Affymetrix GeneChip® is an example of a genomic microarray. The goals of genomic and proteomic microarrays are to make high-throughput genome analysis faster and cheaper, as well as identify activated genes and their sequences. There are many different types of biological entities used in microarrays, but in general the microarray consists of an ordered collection of microspots each containing a single defined molecular species that interacts with the analyte for simultaneous testing of thousands of parameters in a single experiment. Some applications of genomic and proteomic microarrays are neonatal screening, identifying disease risk, and predicting therapy efficacy for personalized medicine.
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With LILBID the analyte is transferred into the mass spectrometer in small droplets (30 or 50 µm diameter) of the sample solution produced by a piezo- driven droplet generator and is desorbed from the aqueous solution by irradiation with a mid-IR laser. This results in biomolecular ions with lower, more native-like charge states in comparison to nESI. At ultra-soft desorption conditions, even weakly interacting subunits of large protein complexes remain associated, so that the mass of the whole complex can be determined. At higher laser intensities, the complex dissociates by thermolysis and subunit masses are recorded.
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Nanosensors are nanoscale devices that measure physical quantities and convert these to signals that can be detected and analyzed. There are several ways proposed today to make nanosensors; these include top-down lithography, bottom-up assembly, and molecular self-assembly. There are different types of nanosensors in the market and in development for various applications, most notably in defense, environmental, and healthcare industries. These sensors share the same basic workflow: a selective binding of an analyte, signal generation from the interaction of the nanosensor with the bio-element, and processing of the signal into useful metrics.
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The MeCAT labelling allows relative and absolute quantification of all kind of proteins or other biomolecules like peptides. MeCAT comprises a site-specific biomolecule tagging group with at least a strong chelate group which binds metals. The MeCAT labelled proteins can be accurately quantified by ICP-MS down to low attomol amount of analyte which is at least 2–3 orders of magnitude more sensitive than other mass spectrometry based quantification methods. By introducing several MeCAT labels to a biomolecule and further optimization of LC-ICP-MS detection limits in the zeptomol range are within the realm of possibility.
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In electrospray ionization (ESI), coeluted matrix components can influence signal intensity through a competition for available charges and for the access to the droplet surface for gas-phase emission, thus creating the so-called matrix effects. Matrix effects can occur at different stages of the interfacing process leading to unpredictably enhanced or suppressed signal response. Direct-EI interface, using a gas phase ionization technique, can eliminate most matrix effects observed with ESI. In fact, it is influenced neither by the mobile phase nor by other matrix components so that the signal response is always proportional only to analyte concentration.
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The original MALDESI design was implemented using organic matrices, similar to those used in MALDI, along with a UV laser. The more recent MALDESI source uses a thin layer of ice as the energy-absorbing matrix that is resonantly excited using a mid-infrared (IR) laser. The IR-MALDESI source can be used for mass spectrometry imaging (MSI), a technique using MS data collected over the sample area to visualize the spatial distribution of specific analyte molecules. A versatile IR-MALDESI MSI source was designed and implemented, which is currently coupled to a high resolving power hybrid Quadrupole-Orbitrap mass spectrometer.
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The source has single- or multi-shot capabilities with adjustable laser fluence, repetition rate, as well as the delay between the laser trigger and MS ion accumulation. The sample plate and moving components are enclosed in a nitrogen purged enclosure where ambient ions and relative humidity can be regulated. A water cooled Peltier thermoelectric plate is used to control the sample temperature (−10 °C to 80 °C). The IR-MALDESI source is currently used to investigate the fundamentals of the ionization process, in addition to being routinely employed for visualizing analyte distributions in biological, forensic, and pharmaceutical samples.
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Another example of portable optical air sensors can involve fluorescence. One example of a fluorescence based sensor is an electronic nose, which can measure analytes in vapor or air. It operates so that an analyte is detected by different sensors in different ways to ensure what is being measured can be differentiated. As the vapor flows into the system it is hit with a high intensity light so that different organic dyes located in different small holes, or micropores, emit a certain wavelength and varied intensity of light based on what vapor compound they are in contact with.
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The primary concern is the concentration of analyte. If the concentration is too high then separation can be unsuccessful, but mass spectrometry as a detection method does not need complete separation, showing another benefit of coupling LC to a mass spectrometer. LC can be coupled to mass spectrometry through the vaporization of the liquid samples as they enter the mass spectrometer. This method can allow for ionization methods that require gaseous samples to be used, such as CI or PI, particularly atmospheric-pressure chemical ionization or atmospheric pressure photoionization, which allows for more interactions and more ionization.
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Concentration overpotential spans a variety of phenomena that involve the depletion of charge-carriers at the electrode surface. Bubble overpotential is a specific form of concentration overpotential in which the concentration of charge- carriers is depleted by the formation of a physical bubble. The "diffusion overpotential" can refer to a concentration overpotential created by slow diffusion rates as well as "polarization overpotential", whose overpotential is derived mostly from activation overpotential but whose peak current is limited by diffusion of analyte. The potential difference is caused by differences in the concentration of charge-carriers between bulk solution and the electrode surface.
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A flame during the assessment of calcium ions in a flame photometerA sample of a material (analyte) is brought into the flame as a gas, sprayed solution, or directly inserted into the flame by use of a small loop of wire, usually platinum. The heat from the flame evaporates the solvent and breaks intramolecular bonds to create free atoms. The thermal energy also excites the atoms into excited electronic states that subsequently emit light when they return to the ground electronic state. Each element emits light at a characteristic wavelength, which is dispersed by a grating or prism and detected in the spectrometer.
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MALDI mass spectrometry is a laser-based soft- ionization method often used for analysis of large proteins, but has been used successfully for lipids. The lipid is mixed with a matrix, such as 2,5-dihydroxybenzoic acid, and applied to a sample holder as a small spot. A laser is fired at the spot, and the matrix absorbs the energy, which is then transferred to the analyte, resulting in ionization of the molecule. MALDI- Time-of-flight (MALDI-TOF) MS has become a very promising approach for lipidomics studies, particularly for the imaging of lipids from tissue slides.
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Wax printing hydrophobic barriers is a common method for creating distinct flow channels within paper devices, and this has been extended to μPAD-MS to enhance ionization efficiency (by enabling focusing of the analyte stream) and enable reaction mixing by wax printing on the triangular paper surface. Chromatographic separations have also been demonstrated on μPADs prior to paper-spray detection. Initially, paper-spray ionization was applied for the detection of small molecules, such as pharmaceuticals and drugs of abuse. However, it has also been shown that paper-spray ionization can ionize large proteins while retaining non-covalent interactions.
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The angle of the incidence light for surface plasmon resonance, an interaction between light wave and conducting electrons in metal, changes when other substances are bounded to the metal surface. Because gold is very sensitive to its surroundings' dielectric constant, binding of an analyte would significantly shift gold nanoparticle's SPR and therefore allow more sensitive detection. Gold nanoparticle could also amplify the SPR signal. When the plasmon wave pass through the gold nanoparticle, the charge density in the wave and the electron I the gold interacted and resulted in higher energy response, so called electron coupling.
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LA-ICP-MS function optimally with gold particles greater than 60 μm in diameter to avoid any contamination during measurements. Although LA-ICP-MS has a lower detection limit, its overall precision was lower than other analysis techniques for trace element concentrations such as field emission-electron probe microanalysis (FE-EPMA) and synchrotron micro X-ray fluorescence spectroscopy (SR-l-XRF). Due to the small size of gold (<5μm-250μm) small fragments of minerals need to be separated from the gold before analysis can occur. Gold fingerprinting has limitations including elemental fractionation (the non-sample related analyte) and calibration requires matrix-matched standards.
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The presence of precipitating agent means that extra washing is required. Filtration should be done in appropriate sized Gooch or ignition filter paper. 5\. Drying and Ignition: The purpose of drying (heating at about 120-150 oC in an oven) or ignition in a muffle furnace at temperatures ranging from 600-1200 oC is to get a material with exactly known chemical structure so that the amount of analyte can be accurately determined. 6\. Precipitation from Homogeneous Solution: To make Q minimum we can, in some situations, generate the precipitating agent in the precipitation medium rather than adding it.
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Chromatography column In analytical and organic chemistry, elution is the process of extracting one material from another by washing with a solvent; as in washing of loaded ion-exchange resins to remove captured ions. In a liquid chromatography experiment, for example, an analyte is generally adsorbed, or "bound to", an adsorbent in a liquid chromatography column. The adsorbent, a solid phase (stationary phase), is a powder which is coated onto a solid support. Based on an adsorbent's composition, it can have varying affinities to "hold" onto other molecules—forming a thin film on the surface of its particles.
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Magnetic immunoassay (MIA) is a novel type of diagnostic immunoassay using magnetic beads as labels in lieu of conventional enzymes (ELISA), radioisotopes (RIA) or fluorescent moieties (fluorescent immunoassays) to detect a specified analyte.MIA involves the specific binding of an antibody to its antigen, where a magnetic label is conjugated to one element of the pair.The presence of magnetic beads is then detected by a magnetic reader (magnetometer) which measures the magnetic field change induced by the beads. The signal measured by the magnetometer is proportional to the analyte (virus, toxin, bacteria, cardiac marker, etc.) concentration in the initial sample.
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The thermal conductivity detector (TCD), also known as a katharometer, is a bulk property detector and a chemical specific detector commonly used in gas chromatography.Grob, Robert L. Ed.; "Modern Practice of Gas Chromatography", John Wiley & Sons, C1977, pg. 228, This detector senses changes in the thermal conductivity of the column effluent and compares it to a reference flow of carrier gas. Since most compounds have a thermal conductivity much less than that of the common carrier gases of helium or hydrogen, when an analyte elutes from the column the effluent thermal conductivity is reduced, and a detectable signal is produced.
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The sample mixture to be separated and analyzed is introduced, in a discrete small volume (typically microliters), into the stream of mobile phase percolating through the column. The components of the sample move through the column at different velocities, which are a function of specific physical interactions with the adsorbent (also called stationary phase). The velocity of each component depends on its chemical nature, on the nature of the stationary phase (column) and on the composition of the mobile phase. The time at which a specific analyte elutes (emerges from the column) is called its retention time.
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Since this is a different species with different diffusion characteristics (and different half-reaction), the slope of current versus added titrant will have a different slope after the equivalence point. This change in slope marks the equivalence point, in the same way that, for instance, the sudden change in pH marks the equivalence point in an acid-base titration. The electrode potential may also be chosen such that the titrant is reduced, but the analyte is not. In this case, the presence of excess titrant is easily detected by the increase in current above background (charging) current.
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Therefore, a buffer solution may be added to the titration chamber to maintain the pH. In instances where two reactants in a sample may react with the titrant and only one is the desired analyte, a separate masking solution may be added to the reaction chamber which eliminates the effect of the unwanted ion. Some reduction-oxidation (redox) reactions may require heating the sample solution and titrating while the solution is still hot to increase the reaction rate. For instance, the oxidation of some oxalate solutions requires heating to to maintain a reasonable rate of reaction.
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Affinity-based capillary electrophoresis, also known as capillary electroaffinity chromatography (CEC), involves the binding of analyte in sample to an immobilized receptor molecule on the capillary wall, microbeads, or microchannels. CEC offers the highest separation efficacy of all three ACE techniques as non-matrixed sample components are washed away and the ligand then be released and analyzed. Affinity capillary electrophoresis takes the advantages of capillary electrophoresis and applies them to the study of protein interactions. ACE is advantageous because it has a high separation efficiency, has a shorter analysis time, can be run at physiological pH, and involves low consumption of ligand/molecules.
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Photographic sequence of a column chromatography The particle size of the stationary phase is generally finer in flash column chromatography than in gravity column chromatography. For example, one of the most widely used silica gel grades in the former technique is mesh 230 – 400 (40 – 63 µm), while the latter technique typically requires mesh 70 – 230 (63 – 200 µm) silica gel. A spreadsheet that assists in the successful development of flash columns has been developed. The spreadsheet estimates the retention volume and band volume of analytes, the fraction numbers expected to contain each analyte, and the resolution between adjacent peaks.
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Schematic of field desorption ionization with emitter at left and mass spectrometer at right Field desorption (FD) is a method of ion formation used in mass spectrometry (MS) in which a high-potential electric field is applied to an emitter with a sharp surface, such as a razor blade, or more commonly, a filament from which tiny "whiskers" have formed. This results in a high electric field which can result in ionization of gaseous molecules of the analyte. Mass spectra produced by FD have little or no fragmentation because FD is a soft ionization method. They are dominated by molecular radical cations M+. and less often, protonated molecules [{M}+H]+.
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However, as a finite droplet exists on the tip of the needle, following the depletion of surface-active analytes, the remaining components in the droplet can then be ionized and observed. This can result in the production of distinctively different mass spectra from a single sample over the application of the high voltage for just a few seconds. This effect offers a particular advantage in the analysis of analytes suffering from ion suppression effects. The presence of surface-active analytes or charged solvent additives can result in the suppressed ionization of analytes of interest, resulting in low sensitivity or the complete absence of the analyte.
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The based of based the probe is briefly touched to the sample surface, where a convex solvent meniscus forms between the probe and the sample, wetting the sample and enabling analyte extraction. The chemistry of the solvent can be modified to induce the extraction of particular analytes of interest. After application to the sample, the sfPESI probe is then raised to be level with the mass spectrometer inlet, with solubilised analytes held in the droplet at the tip of the needle, and a high voltage applied. sfPESI offers the same advantages as standard PESI, including the sequential and exhaustive ionization phenomenon, whilst enabling the direct analysis of dry samples.
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Size-exclusion chromatography (SEC) is also known as gel permeation chromatography (GPC) or gel filtration chromatography and separates molecules according to their size (or more accurately according to their hydrodynamic diameter or hydrodynamic volume). Smaller molecules are able to enter the pores of the media and, therefore, molecules are trapped and removed from the flow of the mobile phase. The average residence time in the pores depends upon the effective size of the analyte molecules. However, molecules that are larger than the average pore size of the packing are excluded and thus suffer essentially no retention; such species are the first to be eluted.
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Disk reading is based on capturing analog signals with the disk drive. The signals are indicative of how much analyte is in a sample. Because the disk spins, the platform has the ability to drive the sample through it through microfluidic channels and for multiple steps to be performed, allowing the possibility for sample preparation and more than one analysis to be conducted during a single run. CD/DVD based assays could potentially be used for any immunoassay already in use and many assays used in analytical chemistry, as long as analytes have a corresponding probe, are soluble, and are large enough to alter the angle of incident.
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In addition to the ability to label and identify individual cells via fluorescent antibodies, cellular products such as cytokines, proteins, and other factors may be measured as well. Similar to ELISA sandwich assays, cytometric bead array (CBA) assays use multiple bead populations typically differentiated by size and different levels of fluorescence intensity to distinguish multiple analytes in a single assay. The amount of the analyte captured is detected via a biotinylated antibody against a secondary epitope of the protein, followed by a streptavidin-R-phycoerythrin treatment. The fluorescent intensity of R-phycoerythrin on the beads is quantified on a flow cytometer equipped with a 488 nm excitation source.
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In this set up helium or nitrogen serve as the carrier gas because of their relatively high thermal conductivity which keep the filament cool and maintain uniform resistivity and electrical efficiency of the filament. However, when analyte molecules elute from the column, mixed with carrier gas, the thermal conductivity decreases and this causes a detector response. The response is due to the decreased thermal conductivity causing an increase in filament temperature and resistivity resulting in fluctuations in voltage. Detector sensitivity is proportional to filament current while it is inversely proportional to the immediate environmental temperature of that detector as well as flow rate of the carrier gas.
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The schematic of IR-MALDESI imaging source Matrix-assisted laser desorption electrospray ionization (MALDESI) is an ambient ionization technique which combines the benefits of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). MALDESI was introduced in 2006 as the first hybrid ionization source combining laser ablation and electrospray post- ionization using a resonantly excited matrix (endogenous or exogenous). An infrared (IR) or ultraviolet (UV) laser can be utilized in MALDESI in order to resonantly excite an endogenous or exogenous matrix. The term ‘matrix’ refers to any molecule that is present in large excess and absorbs the energy of the laser, facilitating desorption of analyte molecules.
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CI has a larger mass range than that of EI and can analyze molecules that EI may not be able to . CI also has the advantage of being less damaging to the sample molecule, so that less fragmentation occurs and more information about the original analyte can be determined. Photoionization (PI) was a method that was first applied as an ionization method to detecting gases separated by GC. Years later, it was also applied as a detector for LC, though the samples must be vaporized first to be detected by the photoionization detector. Eventually PI was applied to mass spectrometry, particularly as an ionization method for gas chromatography-mass spectrometry.
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The "hard ionization" process of electron ionization can be softened by the cooling of the molecules before their ionization, resulting in mass spectra that are richer in information.SMB-MS (Supersonic GC-MS). tau.ac.il In this method named cold electron ionization (cold-EI) the molecules exit the GC column, mixed with added helium make up gas and expand into vacuum through a specially designed supersonic nozzle, forming a supersonic molecular beam (SMB). Collisions with the make up gas at the expanding supersonic jet reduce the internal vibrational (and rotational) energy of the analyte molecules, hence reducing the degree of fragmentation caused by the electrons during the ionization process.
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The specialist will attempt to confirm the diagnosis by repeating the tests by a different method or laboratory, or by performing other corroboratory or disproving tests. The confirmatory test varies depending on the positive results on the initial screen. Confirmatory testing can include analyte specific assays to confirm any elevations detected, functional studies to determine enzyme activity, and genetic testing to identify disease-causing mutations. In some cases, a positive newborn screen can also trigger testing on other family members, such as siblings who did not undergo newborn screening for the same condition or the baby's mother, as some maternal conditions can be identified through results on the baby's newborn screen.
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Ions that are not neutralized by recombination with photoelectrons or counter ions are the so-called lucky survivors. The thermal model postulates that the high temperature facilitates the proton transfer between matrix and analyte in melted matrix liquid. Ion-to-neutral ratio is an important parameter to justify the theoretical model, and the mistaken citation of ion-to-neutral ratio could result in an erroneous determination of the ionization mechanism. The model quantitatively predicts the increase in total ion intensity as a function of the concentration and proton affinity of the analytes, and the ion-to-neutral ratio as a function of the laser fluences.
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A simple interaction experiment involves immobilizing one molecule of a binding pair on the sensor chip surface ("ligand", in Biacore parlance) and injecting a series of concentrations of its partner ("analyte") across the surface. Changes in the index of refraction at the surface where the binding interaction occurs are detected by the hardware and recorded as RU (resonance units) in the control software. Curves are generated from the RU trace and are evaluated by fitting algorithms which compare the raw data to well-defined binding models. These fits allow determination of a variety of thermodynamic constants, including the apparent affinity of the binding interaction.
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Mean pharmacokinetic parameters and their standard deviations were computed for each analyte. Comparative bioavailability and absence of drug-drug interaction for each component were computed based on a point estimate of test/reference (T/R) ratio of geometric means falling within 80-125% for Cmax, AUC0-t and AUC0-∞. The ratio of Cmax, AUC0-t and AUC0-∞ for Polycap and reference drugs was within 80-125% for atenolol, hydrochlorothiazide, ramipril, ramiprilat and dose normalized salicylic acid. However, for simvastatin the point estimate of Cmax, AUC0-t and AUC0-∞ for Ln- transformed data were significantly lower (~25%) and for its active metabolite, simvastatin acid, it was significantly higher (~60%).
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Thus, it is not possible to directly pump the eluate from the LC column into the MS source. Overall, the interface is a mechanically simple part of the LC-MS system that transfers the maximum amount of analyte, removes a significant portion of the mobile phase used in LC and preserves the chemical identity of the chromatography products (chemically inert). As a requirement, the interface should not interfere with the ionizing efficiency and vacuum conditions of the MS system. Nowadays, most extensively applied LC-MS interfaces are based on atmospheric pressure ionization (API) strategies like electrospray ionization (ESI), atmospheric- pressure chemical ionization (APCI), and atmospheric pressure photo-ionization (APPI).
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Because of the high frequency of the light, and the substantial charge and energy of emitted electrons, photoemission is one of the most sensitive and accurate techniques for measuring the energies and shapes of electronic states and molecular and atomic orbitals. Photoemission is also among the most sensitive methods of detecting substances in trace concentrations, provided the sample is compatible with ultra-high vacuum and the analyte can be distinguished from background. Typical PES (UPS) instruments use helium gas sources of UV light, with photon energy up to 52 eV (corresponding to wavelength 23.7 nm). The photoelectrons that actually escaped into the vacuum are collected, slightly retarded, energy resolved, and counted.
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During the fission, the droplet loses a small percentage of its mass (1.0–2.3%) along with a relatively large percentage of its charge (10–18%). There are two major theories that explain the final production of gas-phase ions: the ion evaporation model (IEM) and the charge residue model (CRM). The IEM suggests that as the droplet reaches a certain radius the field strength at the surface of the droplet becomes large enough to assist the field desorption of solvated ions. The CRM suggests that electrospray droplets undergo evaporation and fission cycles, eventually leading progeny droplets that contain on average one analyte ion or less.
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An immunoassay is a biochemical test that measures the presence or concentration of a macromolecule or a small molecule in a solution through the use of an antibody (usually) or an antigen (sometimes). The molecule detected by the immunoassay is often referred to as an "analyte" and is in many cases a protein, although it may be other kinds of molecules, of different size and types, as long as the proper antibodies that have the adequate properties for the assay are developed. Analytes in biological liquids such as serum or urine are frequently measured using immunoassays for medical and research purposes. Immunoassays come in many different formats and variations.
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To generate a standard of known clumped isotope composition, current practice is to internally equilibrate analyte gas at high temperatures in the presence of a metal catalyst and assume that it has the Δ value predicted by equilibrium calculations. Developing isotopic reference materials specifically for clumped isotope analysis remains an ongoing goal of this rapidly developing field and was a major discussion topic during the 6th International Clumped Isotopes Workshop in 2017. It is possible that researchers in the future will measure clumped isotope ratios against internationally distributed reference materials, similar to the current method of measuring the bulk isotope composition of unknown samples.
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Peroxynitrate chemical ionization mass spectrometer at the US National Oceanic and Atmospheric Administration CI mass spectrometry is a useful tool in structure elucidation of organic compounds. This is possible with CI, because formation of [M+1]+ eliminates a stable molecule, which can be used to guess the functional groups present. Besides that, CI facilitates the ability to detect the molecular ion peak, due to less extensive fragmentation. Chemical ionization can also be used to identify and quantify an analyte present in a sample, by coupling chromatographic separation techniques to CI such as gas chromatography (GC), high performance liquid chromatography (HPLC) and capillary electrophoresis (CE).
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These are typically produced by homogenization of a naturally occurring material followed by measurement of each analyte. Due to the difficulty in production and value assignment, these are usually produced by national or transnational metrology institutes like NIST (USA), BAM (Germany), KRISS (Korea) and EC JRC ( European Commission Joint Research Centre). For natural materials, homogenization is often critical; natural materials are rarely homogeneous on the scale of grams so production of a solid natural matrix reference material typically involves processing to a fine powder or paste. Homogenization can have adverse effects, for example on proteins, so producers must take care not to over-process materials.
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TTGE profiles representing the bifidobacterial diversity of fecal samples from two healthy volunteers (A and B) before and after AMC (Oral Amoxicillin- Clavulanic Acid) treatment Denaturing gels are run under conditions that disrupt the natural structure of the analyte, causing it to unfold into a linear chain. Thus, the mobility of each macromolecule depends only on its linear length and its mass-to-charge ratio. Thus, the secondary, tertiary, and quaternary levels of biomolecular structure are disrupted, leaving only the primary structure to be analyzed. Nucleic acids are often denatured by including urea in the buffer, while proteins are denatured using sodium dodecyl sulfate, usually as part of the SDS-PAGE process.
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As light passes from a sample through the element, the normalized intensity, which is detected by a broad band detector, is proportional to the dot product of the regression vector with that spectrum, i.e. is proportional to the concentration of the analyte for which the regression vector was designed. The quality of the analysis is then equal to the quality of the regression vector which is encoded. If the resolution of the regression vector is encoded to the resolution of the laboratory instrument from which that regression vector was designed and the resolution of the detector is equivalent, then the measurement made by Multivariate Optical Computing will be equivalent to that laboratory instrument by conventional means.
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Ionization of the substrate is very efficient as it occurs at atmospheric pressure, and thus has a high collision frequency. Additionally, APCI considerably reduces the thermal decomposition of the analyte because of the rapid desolvation and vaporization of the droplets in the initial stages of the ionization. This combination of factors most typically results in the production of ions of the molecular species with fewer fragmentations than many other ionization methods, making it a soft ionization method. Another advantage to using APCI over other ionization methods is that it allows for the high flow rates typical of standard bore HPLC (0.2-2.0mL/min) to be used directly, often without diverting the larger fraction of volume to waste.
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This utilises a property of and other materials; specifically that a thin layer of gold on a high refractive index glass surface can absorb laser light, producing electron waves (surface plasmons) on the gold surface. This occurs only at a specific angle and wavelength of incident light and is highly dependent on the surface of the gold, such that binding of a target analyte to a receptor on the gold surface produces a measurable signal. Surface plasmon resonance sensors operate using a sensor chip consisting of a plastic cassette supporting a glass plate, one side of which is coated with a microscopic layer of gold. This side contacts the optical detection apparatus of the instrument.
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This is differentiated from calorimetric titrimetry by the fact that the heat of the reaction (as indicated by temperature rise or fall) is not used to determine the amount of analyte in the sample solution. Instead, the equivalence point is determined by the rate of temperature change. Because thermometric titrimetry is a relative technique, it is not necessary to conduct the titration under isothermal conditions, and titrations can be conducted in plastic or even glass vessels, although these vessels are generally enclosed to prevent stray draughts from causing "noise" and disturbing the endpoint. Because thermometric titrations can be conducted under ambient conditions, they are especially well-suited to routine process and quality control in industry.
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In CEC positive ions of the electrolyte added along with the analyte accumulate in the electrical double layer of the particles of the column packing on application of an electric field they move towards the cathode and drag the liquid mobile phase with them. The relationship between the linear velocity u of the liquid in the capillary and the applied electric field is given by the Smoluchowski equation as : u = \epsilon_r\epsilon_0 \zeta E \eta where ζ is the potential across the Stern layer (zeta potential), E is the electric field strength, and η is the viscosity of the solvent. Separation of components in CEC is based on interactions between the stationary phase and differential electrophoretic migration of solutes.
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We have to distinguish between line source AAS (LS AAS) and continuum source AAS (CS AAS). In classical LS AAS, as it has been proposed by Alan Walsh, the high spectral resolution required for AAS measurements is provided by the radiation source itself that emits the spectrum of the analyte in the form of lines that are narrower than the absorption lines. Continuum sources, such as deuterium lamps, are only used for background correction purposes. The advantage of this technique is that only a medium-resolution monochromator is necessary for measuring AAS; however, it has the disadvantage that usually a separate lamp is required for each element that has to be determined.
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Generally, the charges on dissolved molecules and macromolecules are screened by dissolved counterions, since in most cases molecules bound to the devices are separated from the sensor surface by approximately 2–12 nm (the size of the receptor proteins or DNA linkers bound to the sensor surface). As a result of the screening, the electrostatic potential that arises from charges on the analyte molecule decays exponentially toward zero with distance. Thus, for optimal sensing, the Debye length must be carefully selected for nanowire FET measurements. One approach of overcoming this limitation employs fragmentation of the antibody-capturing units and control over surface receptor density, allowing more intimate binding to the nanowire of the target protein.
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Because of the minimal contributions from non-faradaic currents, the use of a differential current plot instead of separate forward and reverse current plots, and significant time evolution between potential reversal and current sampling, high sensitivity screening can be obtained utilizing SWV. For this reason, squarewave voltammetry has been utilized in numerous electrochemical measurements and can be viewed as an improvement to other electroanalytical techniques. For instance, SWV suppressed background currents much more effectively than cyclic voltammetry - for this reason, analyte concentrations on the nanomolar scale can be registered utilizing SWV over CV. SWV analysis has been used recently in the development of a voltammetric catechol sensor,Mersal, G. Int. J. Electrochem. Sci. 4(2009), 1167-1177.
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Core shell fibers of nano particles with fluid cores and solid shells can be used to entrap biological objects such as proteins, viruses or bacteria in conditions which do not affect their functions. This effect can be used among others for biosensor applications. For example, Green Fluorescent Protein is immobilized in nanostructured fibres providing large surface areas and short distances for the analyte to approach the sensor protein. With respect to using such fibers for sensor applications fluorescence of the core shell fibers was found to decay rapidly as the fibers were immersed into a solution containing urea: urea permeates through the wall into the core where it causes denaturation of the GFP.
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A chromatogram of complex mixture (perfume water) obtained by reversed phase HPLC Reversed phase HPLC (RP-HPLC) has a non-polar stationary phase and an aqueous, moderately polar mobile phase. One common stationary phase is a silica which has been surface-modified with RMe2SiCl, where R is a straight chain alkyl group such as C18H37 or C8H17. With such stationary phases, retention time is longer for molecules which are less polar, while polar molecules elute more readily (early in the analysis). An investigator can increase retention times by adding more water to the mobile phase; thereby making the affinity of the hydrophobic analyte for the hydrophobic stationary phase stronger relative to the now more hydrophilic mobile phase.
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Often there are chemical species present or necessary at one stage of sample processing that will interfere with the analysis. For example, some air monitoring is performed by drawing air through a small glass tube filled with sorbent particles that have been coated with a chemical to stabilize or derivatize the analyte of interest. The coating may be of such a concentration or characteristics that it would damage the instrumentation or interfere with the analysis. If the sample can be extracted from the sorbent using a nonpolar solvent (such as toluene or carbon disulfide), and the coating is polar (such as HBr or phosphoric acid) the dissolved coating will partition into the aqueous phase.
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Evanescent field methods such as total internal reflection fluorescence microscopy (TIRF) and surface plasmon resonance (SPR) can offer extremely sensitive measurement of analyte binding and bilayer optical properties but can only function when the sample is supported on specialized optically functional materials. Another class of methods applicable only to supported bilayers is those based on optical interference such as fluorescence interference contrast microscopy (FLIC) and reflection interference contrast microscopy (RICM) or interferometric scattering microscopy (iSCAT). When the bilayer is supported on top of a reflective surface, variations in intensity due to destructive interference from this interface can be used to calculate with angstrom accuracy the position of fluorophores within the bilayer.J M Crane, V Kiessling, and L K Tamm.
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Affinity capillary electrophoresis (ACE) refers to a number of techniques which rely on specific and nonspecific binding interactions to facilitate separation and detection through a formulary approach in accordance with the theory of electromigration. Using the intermolecular interactions between molecules occurring in free solution or mobilized onto a solid support, ACE allows for the separation and quantitation of analyte concentrations and binding and dissociation constants between molecules. With ACE, scientists hope to develop strong binding drug candidates, understand and measure enzymatic activity, and characterize the charges on proteins. Affinity capillary electrophoresis can be divided into three distinct techniques: non- equilibrium electrophoresis of equilibrated sample mixtures, dynamic equilibrium ACE, and affinity-based ACE.
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Measuring isotopic ratios by mass spectrometry includes multiple steps in which samples can undergo cross-contamination, including during sample preparation, leakage of gas through instrument valves, the generic category of phenomena called 'memory effects', and the introduction of blanks (foreign analyte measured as part of the sample). As a result of these instrument-specific effects the range in measured δ values can be lower than the true range in the original samples. To correct for such scale compression researchers calculate a "stretching factor" by measuring two isotopic reference materials (Coplen, 1988). For the hydrogen system the two reference materials are commonly VSMOW2 and SLAP2, where δ2HVSMOW2 = 0 and δ2HSLAP2 = -427.5 vs. VSMOW.
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The principle of operation of Bio-FET devices based on detecting changes in electrostatic potential due to binding of analyte. This the same mechanism of operation as glass electrode sensors which also detect changes in surface potential but were developed as early as the 1920s. Due to the small magnitude of the changes in surface potential upon binding of biomolecules or changing pH, glass electrodes require a high impedance amplifier which increases the size and cost of the device. In contrast, the advantage of Bio-FET devices is that they operate as an intrinsic amplifier, converting small changes in surface potential to large changes in current (through the transistor component) without the need for additional circuitry.
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Schematic of Inlet ionization In mass spectrometry, matrix-assisted ionization (also inlet ionization) is a low fragmentation (soft) ionization technique which involves the transfer of particles of the analyte and matrix sample from atmospheric pressure (AP) to the heated inlet tube connecting the AP region to the vacuum of the mass analyzer. Initial ionization occurs as the pressure drops within the inlet tube. Inlet ionization is similar to electrospray ionization in that a reverse phase solvent system is used and the ions produced are highly charged, however a voltage or a laser is not always needed. It is a highly sensitive process for small and large molecules like peptides, proteins and lipids that can be coupled to a liquid chromatograph.
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Instead of containing only the luxA and luxB genes, bioreporters can contain all five genes of the lux cassette, thereby allowing for a completely independent light generating system that requires no extraneous additions of substrate nor any excitation by an external light source. So in this bioassay, the bioreporter is simply exposed to a target analyte and a quantitative increase in bioluminescence results, often within less than one hour. Due to their rapidity and ease of use, along with the ability to perform the bioassay repetitively in real time and on-line, makes luxCDABE bioreporters extremely attractive. Consequently, they have been incorporated into a diverse array of detection methodologies ranging from the sensing of environmental contaminants to the real-time monitoring of pathogen infections in living mice.
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A midwife draws blood to measure patients' CD4 count within 20 minutes using the Pima point-of-care CD4 analyzer, in Uganda. The ability to perform medical diagnosis at the bedside or at the point-of-care is important in health care, especially in developing countries where access to centralized hospitals is limited and prohibitively expensive. To this end, point-of-care diagnostic bio-MEMS have been developed to take saliva, blood, or urine samples and in an integrated approach perform sample preconditioning, sample fractionation, signal amplification, analyte detection, data analysis, and result display. In particular, blood is a very common biological sample because it cycles through the body every few minutes and its contents can indicate many aspects of health.
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Such changes can be attributed to ionic strength, pH, hydration and redox reactions, the latter due to the enzyme label turning over a substrate. Field effect transistors, in which the gate region has been modified with an enzyme or antibody, can also detect very low concentrations of various analytes as the binding of the analyte to the gate region of the FET cause a change in the drain-source current. Impedance spectroscopy based biosensor development has been gaining traction nowadays and many such devices / developments are found in the academia and industry. One such device, based on a 4-electrode electrochemical cell, using a nanoporous alumina membrane, has been shown to detect low concentrations of human alpha thrombin in presence of high background of serum albumin.
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Secondary ion mass spectrometry (SIMS) was one of the first matrix-free desorption/ionization approaches used to analyze metabolites from biological samples. SIMS uses a high-energy primary ion beam to desorb and generate secondary ions from a surface. The primary advantage of SIMS is its high spatial resolution (as small as 50 nm), a powerful characteristic for tissue imaging with MS. However, SIMS has yet to be readily applied to the analysis of biofluids and tissues because of its limited sensitivity at >500 Da and analyte fragmentation generated by the high-energy primary ion beam. Desorption electrospray ionization (DESI) is a matrix-free technique for analyzing biological samples that uses a charged solvent spray to desorb ions from a surface.
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At its inception as a tool of analytical chemistry, LC-MS/MS spread rapidly and indeed continues to do so in (amongst others) bioanalytical fields, owing to its selectivity for analytes of interest. Indeed, in many cases this selectivity can lead to a misconception that it is always possible to simplify or (on occasion) almost completely remove the necessity for extensive sample preparation. Consequently, LC-MS/MS has become the analytical tool of choice for bioanalysis owing to its impressive sensitivity and selectivity over other, more conventional chromatographic approaches. However, during and after uptake by bioanalytical laboratories worldwide, it became apparent that there were inherent problems with detection of relatively small analyte concentrations in the complex sample matrices associated with biological fluids (e.g.
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In these plasmas the positive ions are almost all singly charged and there are few negative ions, so there are nearly equal amounts of ions and electrons in each unit volume of plasma. What makes Inductively Coupled Plasma Mass Spectrometry (ICP-MS) unique to other forms of inorganic mass spectrometry is its ability to sample the analyte continuously, without interruption. This is in contrast to other forms of inorganic mass spectrometry; Glow Discharge Mass Spectrometry (GDMS) and Thermal Ionization Mass Spectrometry (TIMS), that require a two-stage process: Insert sample(s) into a vacuum chamber, seal the vacuum chamber, pump down the vacuum, energize sample, thereby sending ions into the mass analyzer. With ICP-MS the sample to be analyzed is sitting at atmospheric pressure.
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The estrogen receptor test (ERT) uses the estrogen receptor (ER) tumor marker that allows for immunohistochemical techniques to be performed for diagnostic purposes. Immunohistochemistry (IHC) techniques involve the selective identification of antigen proteins by exploiting these antigen-antibody relationships to characterize your analyte of interest. Previously, the ligand binding assay has been used in the determination of ER activity, however this method was limited because of the requirement of large quantities of fresh tissue needed for each assay. IHC serves as a more efficient methods as this technique allows for the morphology of the tissue to be observed in a tumor- specific manner. This increases the practicability of this technique as in many cases, patients’ tissue samples are limited in the applications of biomarker analysis.
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Amplification of chromosome 9p24 may serve as a predictive biomarker in Hodgkin's lymphoma. Each company pursuing mAbs against PD-1 as drugs developed assays to measure PD-L1 levels as a potential biomarker using their drugs as the analyte-specific reagent in the assay. BMS partnered with Dako on a nivolumab-based assay. However, as of 2015 the complexity of the immune response had hindered efforts to identify people who would be likely to respond well to PD-1 inhibitors; in particular PD-L1 levels appear to be dynamic and modulated by several factors, and efforts to correlate PD-L1 levels before or during treatment with treatment response or duration of response had failed to reveal any useful correlations as of 2015.
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Flame atomic absorption spectroscopy instrument A scientist preparing solutions for atomic absorption spectroscopy, reflected in the glass window of the AAS's flame atomizer cover door Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) is a spectroanalytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation (light) by free atoms in the gaseous state. Atomic absorption spectroscopy is based on absorption of light by free metallic ions. In analytical chemistry the technique is used for determining the concentration of a particular element (the analyte) in a sample to be analyzed. AAS can be used to determine over 70 different elements in solution, or directly in solid samples via electrothermal vaporization, and is used in pharmacology, biophysics, archaeology and toxicology research.
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Dräger was one of a few companies who were early pioneers of colorimetric gas detector tubes (also known as "detector tubes") used to measure the concentration of gases present. In a typical colorimetric gas detector tube a known volume of air is pumped through a tube using a pump. The tube typically has a layer which indicates the analyte by changing colour, depending on the amount of the gas which has passed through the tube the length of the zone which has changed colour will be different. Today colorimetric gas detector tubes are used throughout industry as a low-cost and easy-to-use tool for detecting the presence of gases and are available from a wide range of manufacturers.
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Commercial chloroform-d does, however, still contains a small amount (0.2% or less) of non-deuterated chloroform; this results in a small singlet at 7.26 ppm, known as the residual solvent peak, which is frequently used as an internal chemical shift reference. In carbon-13 NMR spectroscopy, the sole carbon in deuterated chloroform shows a triplet at a chemical shift of 77.16 ppm with the three peaks being about equal size, resulting from splitting by spin coupling to the attached spin-1 deuterium atom (CHCl3 has a chemical shift of 77.36 ppm). It reacts photochemically with oxygen to form phosgene and hydrogen chloride. Therefore, more expensive alternatives like dichloromethane-d2 or benzene-d6 must be used if the analyte is expected to be highly acid-sensitive.
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The separation method that EI is usually coupled with is gas chromatography (GC), where in GC the particles are separated by their boiling points and polarity, followed by solvent extraction of the samples collected on the filters. An alternative to solvent-based extraction for particulates on filters is the use of thermal extraction (TE)-GC/MS, which utilizes oven interfaced with the GC inlet to vaporize the analyte of the sample and into the GC inlet. This technique is more often used then solvent-based extraction, because of its better sensitivity, eliminates need for solvents, and can be fully automated. To increase the separation of the particles the GC can be coupled with a time of flight (TOF)-MS, which is a mass separation method that separates ions based on their size.
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Figure 1 Figure 2 Figure 3 Bio-layer interferometry (BLI) is a label-free technology for measuring biomolecular interactions. It is an optical analytical technique that analyzes the interference pattern of white light reflected from two surfaces: a layer of immobilized protein on the biosensor tip, and an internal reference layer (Figure 1). Any change in the number of molecules bound to the biosensor tip causes a shift in the interference pattern that can be measured in real-time (Figures 1 and 2). The binding between a ligand immobilized on the biosensor tip surface and an analyte in solution produces an increase in optical thickness at the biosensor tip, which results in a wavelength shift, Δλ (Figure 3), which is a direct measure of the change in thickness of the biological layer.
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Once the wells have been treated with ethanol and washed, the cytokine- specific monoclonal capture antibodies can be added to each well. # Cell Incubation: Cell are added to the wells and are incubated in the presence or absence of stimuli that affect protein secretion. # Cytokine Capture: Proteins/analytes that are secreted by the incubated cells will bind to the capture antibodies attached to the wells during the first step. # Detection Antibodies: Similar to the ELISpot, once the wells are rinsed to get rid of the cells and other substances that we are not interested in identifying or measuring, a biotinylated detection antibody is added (this is specific for one type of analyte that you wish to quantify) and then tag-labeled detection antibodies are added for the second and third types of analytes being studied.
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During resonance ionization, an ion gun creates a cloud of atoms and molecules from a gas-phase sample surface and a tunable laser is used to fire a beam of photons at the cloud of particles emanating from the sample (analyte). An initial photon from this beam is absorbed by one of the sample atoms, exciting one of the atom's electrons to an intermediate excited state. A second photon then ionizes the same atom from the intermediate state such that its high energy level causes it to be ejected from its orbital; the result is a packet of positively charged ions which are then delivered to a mass analyzer. Resonance ionization contrasts with resonance-enhanced multiphoton ionization (REMPI) in that the latter is neither selective nor efficient since resonances are seldom used to prevent interference.
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Luminex's Multi-Analyte Profiling (xMAP) technology allows simultaneous analysis of up to 500 bioassays from a small sample volume, typically a single drop of fluid, by reading biological tests on the surface of microscopic polystyrene beads called microspheres. xMAP technology combines this miniaturized liquid array bioassay capability with small lasers, light emitting diodes (LEDs), digital signal processors, photo detectors, charge-coupled device imaging and proprietary software to create a system offering advantages in speed, precision, flexibility and cost. xMAP technology is currently being used within various segments of the life sciences industry, which includes the fields of drug discovery and development, and for clinical diagnostics, genetic analysis, bio-defense, food safety and biomedical research. Luminex MultiCode technology, used for real- time polymerase chain reaction (PCR) and multiplexed PCR assays.
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The single advantage which it brings to a chromatographic purification is that it allows the production of large quantities of highly purified material at a dramatically reduced cost. The cost reductions come about as a result of: the use of a smaller amount of chromatographic separation media stationary phase, a continuous and high rate of production, and decreased solvent and energy requirements. This improved economic performance is brought about by a valve-and-column arrangement that is used to lengthen the stationary phase indefinitely and allow very high solute loadings to the process. In the conventional moving bed technique of production chromatography the feed entry and the analyte recovery are simultaneous and continuous, but because of practical difficulties with a continuously moving bed, the simulated moving bed technique was proposed.
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Because the EFG at the location of a nucleus in a given substance is determined primarily by the valence electrons involved in the particular bond with other nearby nuclei, the NQR frequency at which transitions occur is unique for a given substance. A particular NQR frequency in a compound or crystal is proportional to the product of the nuclear quadrupole moment, a property of the nucleus, and the EFG in the neighborhood of the nucleus. It is this product which is termed the nuclear quadrupole coupling constant for a given isotope in a material and can be found in tables of known NQR transitions. In NMR, an analogous but not identical phenomenon is the coupling constant, which is also the result of an internuclear interaction between nuclei in the analyte.
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These nitrosamine carcinogens are formed from nicotine and related compounds by a nitrosation reaction that occurs during the curing and processing of tobacco. Essentially the plant's natural alkaloids combine with nitrate forming the nitrosamines.Jianxun Zhang et al, Selective Determination of Pyridine Alkaloids in Tobacco by PFTBA Ions/Analyte Molecule Reaction Ionization Ion Trap Mass Spectrometry, Journal of the American Society for Mass Spectrometry, Volume 18, Issue 10, October 2007, Pages 1774-1782 They are called tobacco-specific nitrosamines because they are found only in tobacco products, and possibly in some other nicotine- containing products. The tobacco-specific nitrosamines are present in cigarette smoke and to a lesser degree in "smokeless" tobacco products such as dipping tobacco and chewing tobacco; additional information has shown that trace amounts of NNN and NNK have been detected in e-cigarettes.
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Metastasis is the spread of cancer from one part of the body to another via either the circulatory system or lymphatic system. Unlike radiology imaging tests (mammograms), which send forms of energy (x-rays, magnetic fields, etc.) through the body to only take interior pictures, biosensors have the potential to directly test the malignant power of the tumor. The combination of a biological and detector element allows for a small sample requirement, a compact design, rapid signals, rapid detection, high selectivity and high sensitivity for the analyte being studied. Compared to the usual radiology imaging tests biosensors have the advantage of not only finding out how far cancer has spread and checking if treatment is effective but also are cheaper, more efficient (in time, cost and productivity) ways to assess metastaticity in early stages of cancer.
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Analytical thermal desorption originated in the mid-1970s as an adaptation to the injection procedure for GC. Injector liners were packed with a compound able to adsorb organic compounds, used to sample air or gas, and then dropped into the inlet of the GC. This principle was first widely employed for occupational monitoring, in the form of personal badge-type monitors containing a removable charcoal strip. These offered the advantage of being amenable to analysis without a separate solvent-extraction step. Also developed in the 1970s was a method by which volatiles in the air were collected by diffusion onto tubes packed with a sorbent, which was then heated to release the volatiles into the GC system. These were first introduced for monitoring sulfur dioxide and nitrogen dioxide, but the analyte scope later widened as the sorbents became more advanced.
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Unlike the conventional dried blood spot test for newborn screening that involves a painful heel prick, Metascreen uses urine specimen, collected without harm or discomfort to the newborn, to detect as many as 110 metabolic disorders. The urine specimen is collected on a filter paper, which is then air-dried and sent to the laboratory for analysis using a gas chromatography-mass spectrometry instrument ("GC-MS"). GC-MS is a FDA approved method for urinary analyte detection, a gold standard for lipids, drug metabolites and environmental analysis. Many of the IEMs that are classified as "organic acidemia", in which organic acids accumulate in the urine of newborns with these disorders, are easily and accurately picked up by GC-MS.. The GC-MS platform is recommended by the American College of Medical Genetics for the detection of organic and amino acidemias through the urine.
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A related term was the equivalence factor, one gram divided by equivalent weight, which was the numerical factor by which the mass of precipitate had to be multiplied to obtain the mass of analyte. For example, in the gravimetric determination of nickel, the molar mass of the precipitate bis(dimethylglyoximate)nickel [Ni(dmgH)2] is 288.915(7) , while the molar mass of nickel is 58.6934(2) : hence 288.915(7)/58.6934(2) = 4.9224(1) grams of [Ni(dmgH)2] precipitate is equivalent to one gram of nickel and the equivalence factor is 0.203151(5). For example, 215.3±0.1 mg of [Ni(dmgH)2] precipitate is equivalent to (215.3±0.1 mg) × 0.203151(5) = 43.74±0.2 mg of nickel: if the original sample size was 5.346±0.001 g, the nickel content in the original sample would be 0.8182±0.0004%. Gravimetric analysis is one of the most precise of the common methods of chemical analysis, but it is time-consuming and labour-intensive.
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McNeil's lab at the University of Michigan is known for providing mechanistic understanding to the catalyst transfer polymerization process, helping to show that the likely intermediate is a catalyst-polymer π-complex, but the lab has a diverse focus. For her work on conjugated polymers, there has been considerable focus on expanding the use of catalyst transfer polymerization to make polymers of novel or hard-to-reach architectures (such as conjugated gradient copolymers or insulating-conducting block copolymers) and for studying the properties of new conjugated polymers or new blends of known polymers in solar cells to improve their performance. Another focus has been on molecular gelation; McNeil has published molecular gels as sensors of many harmful or hard to detect compounds. This is with the underlying assumption that it is easier to determine if a gel has formed (since it will go from a flowing solution to a gel that resists flow) rather than alternatives, such as if a solution has changed color (hard to tell if the analyte is strongly colored).
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