Electrochemical oxidation of tiopronin at diamond film electrodes and its determination by amperometric flow injection analysis Original Research Article

The electrooxidation of tiopronin at diamond film electrodes was investigated using cyclic voltammetry. Comparison experiments were performed with glassy carbon electrodes. At the diamond film electrode, it was found that tiopronin provided highly reproducible and well-defined cyclic voltammograms, with peak potential at a potential of +0.8 V versus Ag/AgCl. Conversely, tiopronin gave ill-defined cyclic voltammograms at the glassy carbon electrode. The linearity at diamond film electrode was observed over the range of 0.05–10 mmol l−1 and the detection limit of 50 μmol l−1 (S/B≥3). In addition, the amperometric hydrodynamic voltammetry along with flow injection analysis with diamond electrode as the working electrode was studied. A detection potential of +0.8 V was chosen, at which tiopronin exhibited the highest signal-to-background ratios. The flow injection analysis results showed the significant low detection limit of 10 nmol l−1 (S/N≈3) and a linear dynamic range of 0.5–50 μmol l−1. The method was applied to the determination of tiopronin in a pharmaceutical formulation. According to the procedure based on the standard addition technique, the recoveries obtained were 96.5–108.3% and the RSD values were 1.10–1.62% (n=10).