Electroanalytical determination of sulfadiazine and sulfamethoxazole in pharmaceuticals using a boron-doped diamond electrode

Two sulfonamides, namely sulfadiazine and sulfamethoxazole, were independently quantified in pharmaceutical products by square-wave voltammetry (SWV) using a boron-doped diamond (BDD) electrode. The electroanalytical determination of sulfadiazine was carried out in ethanol + 0.5 mol L−1 H2SO4 50/50 (v/v) and of sulfamethoxazole in ethanol + pH 6.0 phosphate buffer 50/50 (v/v) solutions. Both analytes showed one well-resolved irreversible oxidation peak at around +1.1 V, which served as the analytical response. Calibration curves were obtained in the concentration ranges of 8.01 × 10−6 to 1.19 × 10−4 mol L−1 (r = 0.9995) for sulfadiazine and 6.10 × 10−6 to 6.01 × 10−5 mol L−1 (r = 0.9995) for sulfamethoxazole, with respective detection limits of 2.19 × 10−6 and 1.15 × 10−6 mol L−1. For both sulfonamides, recovery values were in the range of 95–104% for all samples, indicating no matrix interference effects on the analytical results. The accuracy of the electroanalytical methodology reported herein was compared to the standard HPLC method, and the values for the relative error between the proposed and standard methods were −4.31% for sulfadiazine and −0.79% for sulfamethoxazole. The data suggest a potential and interesting alternative method for the electroanalytical determination of sulfa drugs in pharmaceuticals and other products.