Electroanalytical study of sulfa drugs at diamond electrodes and their determination by HPLC with amperometric detection

Conductive boron-doped diamond thin film electrodes were examined for the electroanalysis of three sulfa drugs, sulfadiazine, sulfamerazine and sulfamethazine. Cyclic voltammetry, flow injection analysis and liquid chromatography with electrochemical detection were used to study the oxidation reactions. At diamond electrodes, highly reproducible and well-defined cyclic voltammograms were obtained for all three drugs with a signal to background (S/B) ratio of a factor of ten greater than that obtained at two types of freshly polished glassy carbon (GC) electrodes. Diamond exhibited a highly reproducible amperometric response, with a peak variation of ∼5%, even at a concentration of 100 nM. A detection limit of 50 nM and a linear dynamic range of three orders of magnitude were obtained. No fouling of the electrode was observed within the experimental period of several hours. A rapid stabilization of the background current is achieved, within 10 min after the application of the operating potential under flow conditions, unlike the case of GC electrodes, which requires more than 30 min for reasonable stabilization. We have demonstrated the application of the diamond electrode for the simple and sensitive amperometric detection of the sulfa drugs in a standard mixture after their separation with reverse-phase HPLC to produce chromatograms with a flat baseline and high reproducibility, even at concentrations as low as 100 nM.