DETERMINATION OF THIOLS BY CAPILLARY ELECTROPHORESIS WITH ELECTROCHEMICAL DETECTION USING A PALLADIUM FIELD-DECOUPLER AND CHEMICALLY-MODIFIED ELECTRODES

Off-column electrochemical detection has been used for the determination of cysteine and related compounds after separation by capillary electrophoresis. For the decoupling of the high-voltage field, an improved palladium decoupler was developed with a dead volume of less than 10 nl. Micro-electrodes, bulk-modified with cobalt phthalocyanine, were used in a nanoliter-volume cell for detection of the thiol compounds. With a detection potential of +0.6 V vs. Ag/AgCl a high selectivity and sensitivity was obtained. Baseline separation of cysteine, homocysteine and glutathione could be realized in 25 min, using a formate buffer with pH 2.7 as background electrolyte. Detection limits of 0.5 mu mol l(-1) for homocysteine, 1 mu mol l(-1) for cysteine and 5 mu mol l(-1) for glutathione were obtained. The concentrations of free cysteine and total cysteine (after treatment with dithiothreitol) in urine samples could be measured.