Determination of cysteine and glutathione in plasma and blood by liquid chromatography with electrochemical detection using a chemically modified electrode containing cobalt phthalocyanine.

An assay procedure utilizing amperometric detection at carbon paste electrodes containing cobalt phthalocyanine has been developed for the determination of cysteine and glutathione in blood and plasma samples following preliminary separation by reversed-phase liquid chromatography. The electrocatalytic activity of these chemically modified electrodes permitted optimum response at a potential of +0.75 V vs. Ag/AgCl, several hundred millivolts lower than that required at conventional carbon electrodes. A detection limit of less than 4 pmol was obtained for each compound with minimal sample preparation. In case of fouling of the electrode surface by sample constituents the cobalt phthalocyanine electrode surface could be renewed with a variability of less than 10% and an equilibration time of less than 10 min.