Capillary electrophoresis coupled with 1,1′-thiocarbonyldiimidazole derivatization for the rapid detection of total homocysteine and cysteine in human plasma

•A new CE–UV method for quantification of homocysteine, cysteine and their ratio in plasma was validated.•The time of analysis was 6 min.•Specific derivatization of aminothioles using 1,1′-thiocarbonyldiimidazole.•The method could be used for clinical researches.

A simple and rapid approach is described for the determination of total plasma cysteine and homocysteine using capillary electrophoresis. Human plasma samples were reduced with dithiothreitol and then processed with 1,1′-thiocarbonyldiimidazole in acetonitrile. After centrifugation, the sample supernatant was injected directly into a capillary by applying negative voltage and analytes were stacked after alkaline post-injection. Using a 50 μm i.d. silica capillary of 35 cm total length, filled with 0.1 M triethanolamine, 0.15 M formic acid, and 50 μM hexadecyltrimethylammonium bromide (pH 3.9), we reached a limit of quantification of 2.5 μM for homocysteine. Accuracy was 94.7–105.1%, intra- and inter-day imprecisions were <2.5 and <3%, respectively. The total analysis time was 6 min. Furthermore, liquid-phase extraction with isopropanol led to a fourfold increase in sensitivity.