Microelectrodes, electrophoresis

Tsukahara T, Kuwahata T, Hibara A, Kim HB, Mawatari K, Kitamori T (2009) Electrochemical studies on liquid properties in extended nanospaces using mercury microelectrodes. Electrophoresis 30 3212-3218... 

Conventional colloid chemistry and elaitrochemistry have always been clo ly related with each other, the keywords electrophoresis, double layer theory, and specific adsorption describing typical asp ts of this relationship. In more ro nt times, new aspects have arisen which again bring colloid chemistry into contact with modem developments in electrcolloidal particles as catalysts for electron transfer reactions and as photocatalysts. In fact, the similarity between the reactions that occur on colloidal particles and on compact electrodes has often been emphasized by calling the small particles microelectrodes . 

Nairn, A., and Pretsch, E. (1994). Potentiometric detection of anions separated by capillary electrophoresis using an ion-selective microelectrode. /. Chromatogr. A 676, 437-442. 

Voltammetry has been adapted to HPLC (when the mobile phase is conducting) and capillary electrophoresis (CE) as a detection technique for electroactive compounds. In this usage, the voltammetric cell has to be miniaturised (to about 1 pi) in order not to dilute the analytes after separation. A metal or carbon microelectrode has a defined potential (vs the reference electrode) depending on the substances to be detected (ions or molecules) and the mobile phase flows through the detection cell (Fig. 19.5). This method of amperometric detection in the pulsed mode is very... 

M. L. Kovarik, M.W. Li and R.S. Martin, Integration of a carbon microelectrode with a microfabricated palladium decoupler for use in microchip capillary electrophoresis/ electrochemistry, Electrophoresis, 26 (2005) 202-210. 

G. Chen, L. Zhang and J. Wang, Miniaturized capillary electrophoresis system with a carbon nanotube microelectrode for rapid separation and detection of thiols, Talanta, 64 (2004) 1018-1023. 

UE Spichiger, A Fakler. Potentiometric microelectrodes as sensors and detectors. Magnesium-selective electrodes as sensors, and Hofmeister electrodes as detectors for histamine in capillary electrophoresis. Electrochim Acta 42 3137— 3145, 1997. 

TJ O Shea, SM Lunte. Selective detection of free thiols by capillary electrophoresis-electrochemistry using a gold/mercury amalgam microelectrode. Anal Chem 65 247-250, 1993. 

The detection of the current generated by reaction at the surface of (usually) carbon fiber or copper microelectrodes at a fixed voltage is capable of low detection limits for electroactive compounds using amperometry, Table 8.14. Several approaches that allow the full possibilities of multiple electrode and pulsed amperometric detection (established techniques in liquid chromatography (section 5.7.4)) have been proven for capillary electrophoresis [508,511]. These methods are not widely used, possibly due to a lack of commercial products and support. Potentiometric detection with polymer-coated wire microelectrodes containing relatively non-specific ion exchange ionophores was used for the detection of low-mass anions or cations [510,511]. 

Colon, L. A., Dadoo, R. and Zare, R. N. Determination of carbohydrates by capillary zone electrophoresis with amperometric detection at a copper microelectrode. Anal Chem, 65, 476, 1993. 

Laboratory-on-a-chip systems use immittance and dielectric variables measured with microelectrodes. In flow sensors, cell properties are measured with microelectrodes, and cell characterization and cell separation are performed. Properties of protein molecules have, for many years, been determined by the established methods of electrophoresis. Electrophoresis is based on the electric charge of cells and proteins, and the driving force exerted by an electric field. AU sorts of liquid suspensions with cells or bacteria can be measured with bioimmittance or permittivity. Cell adherence and cell micromotion can be monitored with microelectrodes equipped with a thin surface coating. 

O Shea, T.J. and S.M. Lunte (1994). Chemically modified microelectrodes for capillary electrophoresis/electrochemistry. Anal. Chem. 66(2), 307-311. 

Let us mention that dielectrophoresis has also found wide application in manipulation and sorting of particles and biological cells. Together with standard electrophoresis, it is perhaps the most often used electrokinetic phenomenon with practical applications in mind. Even particle separation can be achieved by using microelectrode arrays [55]. Based on the dielectrophoresis phenomenon, a new technique has recently become available for particle or cell separation, namely the dielectrophoresis/gravitational field-flow fractionation (DEP/G-FFF). In DEP/ G-FFF, the relative positions and velocities of unequal particles or cells are controlled by the dielectric properties of the colloid and the frequency of the applied field. The method has been applied to model polystyrene beads, but, most interestingly, to suspensions of different biological cells [56]. 

See also Electrophoresis Two-Dimensional Gels Nucleic Acids. Enzymes Enzyme-Based Assays. Flow Injection Analysis Principles. Fluorescence Quantitative Analysis. Lab-on-a-Chip Technologies. Mass Spectrometry Matrix-Assisted Laser Desorption/loniza-tion Time-of-Flight. Microelectrodes. Microscopy Overview. pH. Process Analysis Overview Chromatography Electroanalytical Techniques Sensors Acoustic Emission Maintenance, Reliability, and Training. Proteins Overview. Proteomics. Purines, Pyrimidines, and Nucleotides. Sensors Oven/iew. Spectrophotometry Overview. 

W.R. Jin and Y. Wang, Determination of cysteine by capillary zone electrophoresis with end-colunm amperometric detection at a gold/mercury amalgam microelectrode without deoxygenation, J. Chromatogr. A, 1997, 769, 307-314. 

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