Dual electrochemical detection of cysteine and cystine in capillary zone electrophoresis

A method for the simultaneous determination of cysteine and cystine at the submillimolar level is presented based on the capillary zone electrophoretic (CZE) separation of the analytes coupled to a dual electrochemical detection system. The detector uses two gold/mercury amalgam electrodes placed in series and set at -1.00 V and at +0.20 V vs. Ag/AgCl, respectively. The advantages of the proposed method for the analysis of these compounds include direct detection of both analytes, no elaborate sample preparation, no derivatization procedures, and no pathlength dependence. In addition, the small volumes required for CZE analysis make it suitable for clinical studies. The method was applied to human urine samples.