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 corresponding 1,4-diimine which reacts with a range of thiol compounds. The resulting ring substituted (R–S–) diamine is further oxidised leading to an increase in the oxidative current which is proportional to the concentration of the thiol species. The electrode responses were found to be selective towards species including cysteine and homocysteine containing sulfhydryl groups (RSH) with no reaction observed with either methionine (CH3SCH2CH(COOH)NH2) or cystine (cysteine–S–S–cysteine). The potential required to oxidise the ring substituted diamine is found to be dependent upon the nature of the thiol constituent and may allow some scope for speciation studies.