Liquid analysis, amperometry

Another recent development is the advent of pulse amperometry in which the potential is repeatedly pulsed between two (or more) values. The current at each potential or the difference between these two currents ( differential pulse amperometry ) can be used to advantage for a number of applications. Similar advantages can result from the simultaneous monitoring of two (or more) electrodes poised at different potentials. In the remainder of this chapter it will be shown how the basic concepts of amperometry can be applied to various liquid chromatography detectors. There is not one universal electrochemical detector for liquid chromatography, but, rather, a family of different devices that have advantages for particular applications. Electrochemical detection has also been employed with flow injection analysis (where there is no chromatographic separation), in capillary electrophoresis, and in continuous-flow sensors. 

A first interest of MS when used in combination with microfabricated structures, or at the outlet of microfluidic devices, is the match in the volume of liquid handled. A typical MS analysis requires less than 1 pL of liquid, for ESI-MS as well as for MALDI-MS techniques. When working with a continuous flow of liquid and ESI-MS, the MS performance is even more enhanced for flow rates down to 50-100 nL min-1 the lower the flow rate, the better the MS analysis. This flow-rate range corresponds to flow-rate values observed in microfluidic devices. Consequently, the technique of MS is easily scalable and exhibits an enhanced response when the sample size is decreased. This is not the case for instance for other detection techniques, such as UV absorbance or amperometry these two techniques require large detection area or volume, which is the opposite of the quest of microfluidics. This first advantage of MS compared to other technique goes together with its high sensitivity. 

Two other areas where amperometry has played a major role since the 1970s are the detection of various substances in high-performance liquid chromatography and flow injection analysis. To a lesser extent, amperometric detection has also been applied to ion chromatography of anions and cations. 

See also Amperometry. Atomic Emission Spectrometry Flame Photometry. Chemiiuminescence Overview Liquid-Phase. Flow Injection Analysis Principles. Fluorescence Quantitative Analysis. Ion Exchange Ion Chromatography Instrumentation. Liquid Chromatography Overview. Ozone. Sampling Theory. Sulfur. Textiles Natural Synthetic. 

See also Amperometry. Blood and Plasma. Clinical Analysis Sample Handling Inborn Errors of Metabolism. Fluorescence Derivatizatlon Fluorescence Labeling. Gas Chromatography Mass Spectrometry. Isotope Dilution Analysis. Liquid Chromatography Clinical Applications. 

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. 

See alsa Amperometry. Carbohydrates Sugars -Chromatographic Methods. Derivatization of Analytes. Electrophoresis Principles. Flow Injection Analysis Principles. Ion Exchange Principles. Liquid Chromatography Column Technology Chiral Analysis of Amino Acids. Sensors Amperometric Oxygen Sensors. 

See also Air Analysis Sampling Outdoor Air Workplace Air. Amperometry. Chemiluminescence Liquid-Phase Gas-Phase. Coulometry. Remote Gas Sensing Overview. Spectrophotometry Inorganic Compounds. 

See also. Amperometry. Conductimetry and Oscillometry. Coulometry. Electrogravimetry. Ion-Selective Electrodes Oven/iew Glass Solid-State Liquid Membrane Gas Sensing Probes Water Applications. pH. Polarography Overview. Process Analysis Sensors. Sensors Overview Amperometric Oxygen Sensors. Sulfur. Voltammetry Overview Anodic Stripping. Water Analysis Industrial Effluents. 

Note A amperometry BI bead injection CL chemiluminescence F fluorescence FAT flow analysis technique HPLC/DAD high-performance liquid chromatography with diode array detector LOD detection limit MCFIA multicommutated flow injection analysis MPFS multipumping flow systems MSFIA multisyringe FIA P potentiometry RSD relative standard deviation SF sampling frequency SFA stopped-flow analysis SP spectrophotometry. 

A different concept based on amperometry was described by Fasching et al. [45], They have developed a miniaturized amperometric sensor for CO2 in liquids for applications in clinical blood gas analysis. The detection principle is based on the pH-dependent dissociation of copper complexes. Different CO2 concentrations result in corresponding pH shifts of the internal hydrogel electrolyte. These pH variations lead to certain dissociation levels of the copper complexes... 

---