Electrochemically initiated 1,4 additions: a versatile route to the determination of thiols

The electrochemical generation of quinoid intermediates and their subsequent reaction with sulphydryl thiols (RSH) have been investigated as a method by which the latter can be quantified. Nucleophilic addition of the thiol species to the electrogenerated quinoid structure leads to the production of a chemically reduced adduct whose subsequent re-oxidation at the electrode leads to an amplification of the oxidative current. This can be correlated to the concentration of thiol present within the medium. The influence of indicator composition on the nature of the analytical response has been assessed through examining the electrochemical properties of 15 derivatives and the validity of the proposed reaction pathway corroborated by comparison of the voltammetric response with computer simulations. Interference by other electroactive species (ascorbate, urate, tyrosine) and other physiological constituents (cystine, lysine) has also been assessed. (C) 2001 Elsevier Science B.V. All rights reserved.