SIMULTANEOUS DETECTION OF THIOLS AND DISULFIDES BY CAPILLARY ELECTROPHORESIS ELECTROCHEMICAL DETECTION USING A MIXED-VALENCE RUTHENIUM CYANIDE-MODIFIED MICROELECTRODE

Thiols and disulfides are separated and detected by capillary electrophoresis-electrochemical detection using a mixed-valence ruthenium cyanide-modified microelectrode. A carbon fiber array microelectrode was employed to maximize the signal-to-noise ratio. Detection limits for glutathione disulfide, cystine and homocystine were 2.5, 1.3 and 1.1 fmol, respectively. The response for cystine was linear over two orders of magnitude with a correlation coefficient of 0.992. The long-term stability and overall reproducibility of the electrode were investigated and found to be highly dependent on the cation concentration in the electrophoretic buffer. The selectivity of this technique for disulfides was demonstrated by the detection of cystine in the urine of a patient with kidney stones.