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.