Highly sensitive electrocatalytic determination of pyrazinamide using a modified poly(glycine) glassy carbon electrode by square-wave voltammetry

A new voltammetric sensor based on electropolymerization of glycine at glassy carbon electrode (GCE) was developed and applied to determine of pyrazinamide (PZA) by square-wave voltammetry (SWV). The initial cyclic voltammetric studies showed an electrocatalytic activity of poly(Gly)/GCE on redox system of pyrazinamide in 0.1 mol L-1 phosphate buffer solution pH 7.5, with E (Pc) and E (Pa) in -0.85 and -0.8 V (versus E (Ag/AgCl)), respectively. Studies at different scan rates suggest that the redox system of pyrazinamide at poly(Gly)/GCE is a process controlled by diffusion in the interval from 10 to 100 mV s(-1). Square-wave voltammetry-optimized conditions showed a linear response of PZA concentrations in the range from 0.47 to 6.15 mu mol L-1 (R = 0.998) with a limit of detection (LOD) of 0.035 mu mol L-1 and a limit of quantification (LOQ) of 0.12 mu mol L-1. The developed SWV-poly(Gly)/GCE method provided a good intra-day (RSD = 3.75 %) and inter-day repeatability (RSD = 4.96 %) at 4.06 mu mol L-1 PZA (n = 10). No interference of matrix of real samples was observed in the voltammetric response of PZA, and the method was considered to be highly selective for the compound. In the accuracy test, the recovery was found in the range of 98.2 and 104.0 % for human urine samples and pharmaceutical formulation (tablets). The PZA quantification results in pharmaceutical tablets obtained by the proposed SWV-poly(Gly)/GCE method were comparable to those found by official analytical protocols.