Selective determination of thiols: a novel electroanalytical approach

The two electron electro-oxidation of N,N-dimethylphenylene-1,4-diamine and related compounds in aqueous solution leads to the formation of the corres ponding 1,4-diimine which reacts with a range of thiol compounds. The resul ting ring substituted (R-S-) diamine is further oxidised leading to an incr ease in the oxidative current which is proportional to the concentration of the thiol species. The electrode responses were found to be selective towa rds species including cysteine and homocysteine containing sulfhydryl group s (RSH) with no reaction observed with either methionine (CH3SCH2CH(COOH)NH 2) or cystine (cystein-S-S-cysteine). The potential required to oxidise the ring substituted diamine is found to be dependent upon the nature of the t hiol constituent and may allow some scope for speciation studies.