Determination of cysteine by capillary zone electrophoresis with end-column amperometric detection at a gold/mercury amalgam microelectrode without deoxygenation.

Capillary zone electrophoresis was employed for the determination of cysteine using an end-column amperometric detection with a gold/mercury amalgam microelectrode, at a constant potential of 0.02-0.06 V vs. saturated calomel electrode. In this procedure deoxygenation is not necessary. The electrochemical characteristics at the microelectrode, the effect of the concentration of the buffer and the separation voltage across the capillary on the migration time and separation efficiency, and the dependence of the injection voltage and time on the detection signal, the separation efficiency and coulometric efficiency has been investigated. The calibration plot was found to be linear over four orders of magnitude and the limit of detection was 5.8 x 10(-8) mol/l (or 14.5 amol). The method was applied to the determination of cysteine in human plasma, blood and urine.