Simultaneous determination of N-acetyl-L-cysteine (NAC), uric acid (UA) and tryptophan (Trp) has been studied at the surface of glassy carbon electrode (GCE) in the present of 4-chlorocatechol as a homogenous electrochemical catalyst in aqueous media. The electrocatalytic properties of GCE in the present of 4-chlorocatechol toward the electrocatalytic oxidation of NAC, UA and Trp was studied using cyclic voltammetry (CV), double-step potential chronoamperometry and differential pulse voltammetry (DPV). The results show that NAC participates in the reaction with electrogenerated quinone from electrooxidation of 4-chlorocatechol at surface of GCE to form the corresponding thioquinone derivative. The reoxidation of the adduct leads to increase in the oxidative current which is proportional to the concentration of NAC. Differential pulse voltammogram peak currents of NAC, UA and Trp increased linearly with their concentrations in the ranges of 5.0 - 45.0 μM, 10.0 - 50.0 μM and 5.0 - 55.0 μM, respectively and the detection limits for NAC, UA and Trp were sequentially 3.55 μM, 6.96 μM and 4.41 μM. The proposed method was employed for simultaneous determination of NAC, UA and Trp in the pharmaceutical and biological samples and the obtained results were found to be satisfactory.
