Electrochemically driven derivatisation-detection of cysteine

The electrochemical oxidation of catechol to ortho quinone at a glassy carb on electrode in the presence of cysteine is shown to lead to the deposition of a quinone-cysteine adduct at the electrode surface. Square wave voltamm etry is shown to enable voltammetric resolution of unreacted orthoquinone a nd the accumulated adduct species such that quantification of both species is possible over a range of pH 2-pH 6. The reaction is shown to be selectiv e towards cysteine with little interference from cystine, homocysteine or g lutathione. The foundations of a detection protocol are reported with the s ensitivity shown to be capable of attenuation through the facile manipulati on of the number of electro-initiated derivatisation scans. The application of six consecutive derivatisation scans is shown to provide a linear range of 2-20 muM cysteine that is well within the region required for physiolog ical monitoring.