PULSED ELECTROCHEMICAL DETECTION OF CYSTEINE, CYSTINE, METHIONINE, AND GLUTATHIONE AT GOLD ELECTRODES FOLLOWING THEIR SEPARATION BY LIQUID-CHROMATOGRAPHY

A unique PED waveform is applied for detection of the sulfur-containing compounds of interest following their separation on a chromatographic column having both cation-exchange and reversed-phase properties. The mobile phase is 0.10 M HClO4/0.15 M NaClO4/5% MeCN, which results in virtually no PED response for carbohydrates and non-sulfur-containing amino acids. The PED waveform utilizes current integration throughout the period of a fast cyclic potential scan to eliminate the large background current normally observed for the conventional three-step PED waveform as a consequence of formation of surface oxide, which is required by the detection mechanism. Limits of detection for the compounds of interest are at the picomolar level.