Electrochemical detection capillary electrophoresis

Modern tHcy methods include enzyme immunoassays and chromatographic-based methods. In practice, immunoassays " are most often used for routine purposes (e.g., fluorescence polarization immunoassay IFPIA] as run on Abbott s IMx and AxSYM platforms) Chromatographic assays include amino acid analysis high-performance liquid chromatography (HPLC) with ultraviolet, fluorescence, or electrochemical detection ° " capillary electrophoresis with fluorescence detection gas chromatography-mass spectrometry (GC-MS) and liquid chromatography with tandem MS (MS-MS). 

Woods, L. A. and Ewing, A. G, Etched electrochemical detection for electrophoresis in nanometer inner diameter capillaries, Chemphyschem, 4, 207-211, 2003. 

Simple etching of the capillary end served to decouple the electrophoretic current from that of amperometric detection, permitting quantitation of attomole levels of catecholamines from brain microdialyzates.24 A postcolumn reactor using bromine generated electrochemically in situ has been used in the detection of peptide thiols, such as glutathione and cysteine, separated by capillary electrophoresis.25... 

Qian, J., Wu Y., Yang, H., and Michael, A.C., An integrated decoupler for capillary electrophoresis with electrochemical detection application to analysis of brain microdialysate, Anal. Chem. 71, 4486, 1999. 

A.T. Wooley, K. Lao, A.N. Glazer and R.A. Mathias, Capillary electrophoresis chip with integrated electrochemical detection, Anal. Chem.,... 

P. Selvaganapathy, M.A. Burns, D.T. Burke and C.H. Mastrangelo, Inline electrochemical detection for capillary electrophoresis, IEEE, 451-454, 2001. 

Fig. 3.172. Non-aqueous capillary electrophoresis with electrochemical detection of a dye mixture containing (a) 1.7 jUg/ml malachite green, (b) 0.70 jug/ml crystal violet, (c) 4.3 /ig/ml rhodamine B, and (d) 9.1 X 10-6 M ferrocene. Experimental conditions capillary dimensions, 95 cm X 75 pm i.d. running electrolyte, acetonitrile containing 1 M HAc and 10 mM NaAc electrokinetic injection, 20 s 5 kV separation voltage 20 kV applied detection potential, 1.55 V. Reprinted with permission from F.-M. Matysik [206].

F.-M. Matysik, Potentialities of electrochemical detection in conjunction with non-aqueous capillary electrophoresis. Electrochim. Acta, 43 (1998) 3475-3482. 

F.-M. Matysik, Non-aqueous capillary electrophoresis with electrochemical detection. J. Chromatogr.A, 802 (1998) 349-354. 

Haber, C. (1997). Electrochemical detection in capillary electrophoresis. In Handbook of Capillary Electrophoresis (J. P. Landers, Ed.), 2nd Edition, pp. 425—447, CRC Press, Boca Raton. 

A Wang, Y Fang. Applications of capillary electrophoresis with electrochemical detection in pharmaceutical and biomedical analyses. Electrophoresis 21 1281-1290, 2000. 

Although this section provides a brief description of most commonly nsed detectors for HPLC, most of the focus is on a few detection modes. Optical absorbance detectors remain the most widely nsed for HPLC, and are discnssed in some detail. We also focns on flnorescence, condnctivity, and electrochemical detection, as these methods were not widely nsed for HPLC in the past, bnt are especially well suited to micro- and nano-flow instrnments becanse of their high sensitivity in small sample volumes. Mass spectrometry has also come into wide and rontine nse in the last decade, but as it is the subject of another chapter, it will not be fnrther discnssed here. Miniaturization has been particularly important for capillary and chip-based electrophoresis, which often employs sub-nanoliter detection volnmes [36,37]. 

K. M. Walsh, and R. S. Keynton, Fully Integrated On-Chip Electrochemical Detection for Capillary Electrophoresis in a Microfabricated Device, Anal. Chem. 2002, 74, 3690 M. L. Chabinyc, D. T. Chiu, J. C. McDonald, A. D. Strook, J. F. Christian, A. M. Karger, and G. M. Whitesides, An Integrated Fluorescence Detection System in Poly(dimethylsiloxane) for Microfluidic Applications, Anal. Chem 2001, 73, 4491. 

Electrochemical Detection in Liquid Chromatography and Capillary Electrophoresis - 813... 

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. 

Spectroscopic detection techniques (UV, fluorescence) are the most common methods of detection employed in CE. UV detection, although the simplest method of detection to adapt to CE, suffers from a loss of sensitivity due to the extremely small pathlengths involved in CE. Laser-induced fluorescence detection is much more sensitive, but is limited by the number of wavelengths available for excitation. In addition, this technique is very expensive to implement and maintain. Electrochemical detection has several advantages for CE [47]. Since electrochemical detection is based on a reaction at the electrode surface, the cell volume can be very small without loss of sensitivity. The concentration-based limits of detection for capillary electrophoresis with electrochemical detection (CEEC) are comparable to those of LCEC. 

Electrochemical detectors for liquid chromatography have reached a level of maturity in that thousands of these devices are used routinely for a variety of mundane purposes. Nevertheless, the technology is advancing rapidly in several respects. Multiple electrode and voltammetric detectors have been developed for more specialized applications. Small-volume transducers based on carbon fiber electrodes are being explored for capillary and micropacked columns. Recently, electrochemical detection has also been coupled to capillary electrophoresis [47]. Finally, new electrode materials with unique properties are likely to afford improved sensitivity and selectivity for important applications. 

Several techniques have been developed for the determination of purine and pyrimidine derivatives in food sample and in particular for hypoxanthine quantification biosensors (220-223) and electrochemical methods making use of immobilized enzyme electrode (224 -227), electrochemical enzymatic-based HA methods (228,229), enzyme reaction with fluorimetric detection (230), radioimmunoassay (231), colorimetric methods (232), capillary electrophoresis (233), and TLC (234). Many HPLC methods have also been developed and are reported in Table 4 (235-247) the most recent ones are described next. 

Wallingford and Ewing Electrochemical detection in capillary electrophoresis... 

The aim of this chapter is to show through the subsequent sections the present trends in capillary electrophoresis microchips paying special attention to the manufacturing and designs employed in those combined to electrochemical (EC) detection. Conductimetric and amperometric detection are considered. Clinical application of these devices is further revised. 

M. Castano-Alvarez, M.T. Fernandez-Abedul and A. Costa-Garcia, Poly(methylmethacrylate) and Topas capillary electrophoresis microchip performance with electrochemical detection, Electrophoresis, 26 (2005) 3160-3168. 

J. Wang, J. Zima, N.S. Lawrence and M.P. Chatrathi, Microchip capillary electrophoresis with electrochemical detection of thiol-containing degradation products of V-type nerve agents, Anal. Chem., 76 (2004) 4721-4726. 

P. Ertl, C.A. Emrich, P. Singhal and R.A. Mathies, Capillary electrophoresis chips with a sheath-flow supported electrochemical detection system, Anal. Chem., 76 (2004) 3749-3755. 

J. Wang, Electrochemical detection for capillary electrophoresis microchips A review, Electroanalysis, 17 (2005) 1133-1140. 

R.S. Martin, K.L. Ratzlaff, B.H. Huyng and S.M. Lunte, In-channel electrochemical detection for microchip capillary electrophoresis using an electrically isolated potentiostat, Anal. Chem., 74 (2002) 1136-1143. 

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