Simultaneous determination of ethionamide and pyrazinamide using poly(l-cysteine) film-modified glassy carbon electrode.

A selective, simple and rapid square wave voltammetry method, based on electropolymerization of l-cysteine (poly(l-Cys)) on a glassy carbon electrode (GCE), was developed in this study for simultaneous determination of ethionamide and pyrazinamide. Electroanalytical and electrochemical properties of the poly(l-Cys)/GCE were investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM). The cyclic voltammetry studies revealed an remarkable electrocatalytic activity of poly(l-Cys)/GCE on ethionamide and pyrazinamide at pH 1.0. The best potential separation between the reduction peaks of the drugs in a mixed solution was found to be 0.14V. It was also found that pyrazinamide exhibits a reversible wave with Epc and Epa at -404mV and -347mV (versus EAg/AgCl), respectively, while ethionamide presents an irreversible reduction peak at Epc=-536mV. The optimized calibration curves for simultaneous determination of ethionamide and pyrazinamide exhibited good and high linear responses within the concentration range 2.38-248.0µmolL(-1) and 0.476-51.2µmolL(-1), respectively. The limit of detection was found to be 0.531µmolL(-1) for ethionamide and 0.113µmolL(-1) for pyrazinamide. The poly(l-Cys)/GCE-based square wave voltammetry method was successfully used to determine ethionamide and pyrazinamide in human urine and blood serum.