Electrochemical Oxidation of 4-Chlorocatechol in the Presence of Some Sulphydryl Compounds: Applications to Voltammetric Detection of D-Penicillamine, Glutathione and L-Cysteine

Electrooxidation of 4-chlorocatechol at a glassy carbon electrode (GCE) was investigated in the presence of some biologically important thiols (RSH), e.g. Dpenicillamine (D-PA), glutathione (GSH) and L-cysteine (L-Cys) in aqueous media using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and double step potential chronoamperometry methods. The 4-chlorocatechol exhibits strong electrochemical response toward thiols oxidation in wide pH rang (2.00–9.00). The results show that thiol-containing compounds participate in Michael addition reactions with 4-chlorocatechol to form the corresponding thioquinone derivatives. The reoxidation of the adduct leads to an increase in the anodic current. Therefore, in the optimum condition (pH=6.00) in CV, the oxidation of D-PA, GSH and L-Cys in the presence of 4-chlorocatechol occur at a potential about 420, 750 and 420 mV, respectively less positive than that in the absence of it. The kinetic parameters such as electron transfer coefficient, α and electrochemical reaction rate constant, kh was determined using electrochemical approaches.