Measurement of biological thiols and disulfides by high-performance liquid chromatography and electrochemical detection of silver mercaptide formation

A rapid and sensitive method is described for the measurement of picomole levels of the biological thiols glutathione, cysteine, penicillamine, cysteamine, and ergothioneine by a combination of high-performance liquid chromatography and electrochemical detection (ECD). The compounds were separated isocratically on a reversed-phase C18 column by ion-pair chromatography with a mobile phase containing 5 mM acetic acid and 2.5 mM sodium 1-octanesulfonate. After chromatographic separation, the eluate was combined with silver nitrate dissolved in ammonium nitrate buffer at pH 10.5. A platinum disc electrode was used at -0.1 V vs Ag/AgCl to detect the amount of silver ions that had been consumed by the reaction with thiols. For measurement of disulfide, S-sulfonation with sodium sulfite or electroreduction were used to cleave the disulfide, and the thiol anions produced were detected by HPLC-ECD as for the reduced forms. The method was used to assay thiols and disulfides in biological materials.