Standard amperometry

The analytic principles that have been applied to accumulate air quality data are colorimetry, amperometry, chemiluminescence, and ultraviolet absorption. Calorimetric and amperometric continuous analyzers that use wet chemical techniques (reagent solutions) have been in use as ambient-air monitors for many years. Chemiluminescent analyzers, which measure the amount of chemiluminescence produced when ozone reacts with a gas or solid, were developed to provide a specific and sensitive analysis for ozone and have also been field-tested. Ultraviolet-absorption analyzers are based on a physical detection principle, the absorption of ultraviolet radiation by a substance. They do not use chemical reagents, gases, or solids in their operation and have only recently been field-tested. Ultraviolet-absorption analyzers are ideal as transfer standards, but, as discussed earlier, they have limitations as air monitors, because aerosols, mercury vapor, and some hydrocarbons could, interfere with the accuracy of ozone measurements made in polluted air. 

AA and IAA Processed A A + IAA cold Precolumn Spheri- Isocratic 5 mM Amperometry External standardization. 60,... 

GLUCONIC ACID DETERMINATION IN STANDARD SOLUTIONS BY BATCH AMPEROMETRY USING THE BIOSENSOR... 

The enzymatic reaction occurring in the various micro-channels during the detection step is followed by chrono-amperometry as presented in Fig. 50.2A. The measured currents result from the oxidation of the p-aminophenol produced by the enzymes, and it is thus increasing with the reaction time. Finally, the values of the slopes of these current versus time curves (in A/s) are reported as a function of the known concentrations of the IL-1B standards, thereby providing a calibration curve as shown in Fig. 50.2B. 

The quantitation of enzymes and substrates has long been of critical importance in clinical chemistry, since metabolic levels of a variety of species are known to be associated with certain disease states. Enzymatic methods may be used in complex matrices, such as serum or urine, due to the high selectivity of enzymes for their natural substrates. Because of this selectivity, enzymatic assays are also used in chemical and biochemical research. This chapter considers quantitative experimental methods, the biochemical species that is being measured, how the measurement is made, and how experimental data relate to concentration. This chapter assumes familiarity with the principles of spectroscopic (absorbance, fluorescence, chemi-and bioluminescence, nephelometry, and turbidimetry), electrochemical (poten-tiometry and amperometry), calorimetry, and radiochemical methods. For an excellent coverage of these topics, the student is referred to Daniel C. Harris, Quantitative Chemical Analysis (6th ed.). In addition, statistical terms and methods, such as detection limit, signal-to-noise ratio (S/N), sensitivity, relative standard deviation (RSD), and linear regression are assumed familiar Chapter 16 in this volume discusses statistical parameters. 

The accepted reference method for determining chloride in blood serum, plasma, urine, sweat, and other body fluids is the coulometric titration procedure. In this technique, silver ions are generated coulometrically. The silver ions then react with chloride ions to form insoluble silver chloride. The end point is usually detected by amperometry (see Section 23B-4) when a sudden increase in current occurs on the generation of a slight excess of Ag. In principle, the absolute amount of Ag" needed to react quantitatively with Cl can be obtained from application of Faraday s law. In practice, calibration is used. First, the time required to titrate a chloride standard solution with a known number of moles of chloride (nci )s using a constant current I is measured. The same constant current is next used in the titration of the unknown solution, and the time r is measured. The number of moles of chloride in the unknown (ncr)u is then obtained as follows ... 

Lipoic acid acts as one of the coenzymes in the oxidative decarboxylation of pyruvate and other a-keto acids. It can be separated in an alkaline environment on a strongly basic anion exchanger in the hydroxide form, and can be detected like carbohydrates via pulsed amperometry at a Au working electrode. The corresponding chromatogram of a lipoic acid standard is shown in Fig. 8-88. This method allows to accurately detect 0.1 nmol lipoic acid. 

Detection of the molecules produced, consumed, and secreted by the cells described here is challenging for two main reasons. First, the cell is dynamic and constantly tries to maintain balance. As such, molecules concentrations or speciation are usually changing. Second, the matrix in which these measurements are typically performed is very complex. Thus, the technique of choice needs to have some built-in feature that enables the analyst to overcome the matrix. To date, a variety of measurements have been employed to learn more about the roles of the cells in the microcirculation. Specifically, fluorescence, chemiluminescence, and amperometry have all been used extensively. Not surprisingly, all three of these detection schemes are readily employed in capillary electrophoresis-based determinations. Therefore, many of the measurements employ technology from the CE field. However, due to the cell matrix complexity, techniques are required to overcome potential interfer-ents. Eor example, Kovarik et al. employed a Nafion coating over a micromolded ink electrode for selectivity in detecting dopamine in the presence of an anion interferent (ascorbate). Eor similar reasons, Ku" ° employed the classic method of multiple standard additions to quantitatively determine the amount of NO released from activated platelets in a flowing stream. 

Cyanide Chloramine-T/pyridine-barbituric acid Spectrophotometry/ Amperometry 0.002-2.0 mg CN Gas-diffusion preconcentration/UV-photolysis for total cyanide determination/ standard method ISO 14403... 

See also Amperometry. Derivatization of Anaiytes. Food and Nutritional Analysis Meat and Meat Products Dairy Products. Liquid Chromatography Food Applications. Nitrogen. Polarography Inorganic Applications. Quality Assurance Primary Standards. Spectrophotometry Organic Compounds. Sulfur. Vitamins Fat-Soluble Water-Soluble. 

Figure 3.271 Analysis of a collagen hydrolysate and an amino acid/amino sugar standard with anion-exchange chromatography and integrated amperometry. Chromatographic...

Figure 8.18 Analysis of lipoic acid utilizing detection pulsed amperometry on a gold pulsed amperometric detection. Separator col- working electrode injection volume 50pL umn CarboPac PA1 eluent 0.1 mol/L NaOH sample 40 mg/L lipoic acid standard (1).

Figure 10.345 Separation of monosaccharides of a standard (a) and a monoclonal antibody (b). Separator column CarboPac PA1 eluent 16 mmol/L NaOH flow rate 1 mt/min detection pulsed amperometry on a gold working electrode peaks fucose (1), rhamnose as...

Conductivity detection and DC amperometry can be used simultaneously. In a non-suppressed system the conductivity cell effluent is directed to the amperometric cell in a suppressed system the positioning of the amperometric cell depends on the electrode material. The carbon paste electrode, for example, is positioned between the suppressor and the conductivity cell, so that electroactive anions can be detected together with standard anions [14]. An example of applications involving a carbon paste electrode is shown in Fig. 7-8. The separation of nitrite, thiosulfate, and iodide is performed in an acidic medium with a... 

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