Electroanalysis of sulfur-containing compounds using a boron-doped diamond thin-film applied to flow injection

Abstract

The oxidation of sulfur-containing compounds such as cysteine, homocysteine, glutathione, 2-mercaptoethane sulfonic acid and cephalexin, in carbonate buffer, pH 9.2, was investigated using cyclic voltammetry. A boron-doped diamond thin-film was used as the working electrode compared with a glassy carbon electrode. Ag/AgCl electrode was employed as the reference electrode and a platinum wire was used as the counter electrode. The results indicated that a boron-doped diamond was an excellent electrode for detecting sulfur-containing compounds. A peak shape of cyclic voltammogram that received from boron-doped diamond thin-film was well-defined compared to the one from a glassy carbon electrode. A linear dynamic range of 0.5 mM to 10 mM and a detection limit of 0.5 mM were observed except cephalexin, which had a linear dynamic range of 10 mM to 25 mM and a detection limit of 10 mM. The boron-doped diamond thin-films exhibited higher sensitivity than theglassy carbon electrode. However, the oxidative products could cover the surface of electrode and decreased the next scan signal. Flow injection analysis (FIA) was chosen to overcome this problem. FIA with the boron-doped diamond thin-film electrodes provided the reproducible results. A linear dynamic range of cysteine and 2-mercaptoethane sulfonic acid was of 50 nM to 10 (mu), and the detection limit of 50.0 nM at a S/N = 3 was obtained at the boron-doped diamond thin-film. It was found that signals from a home-made flow cell were reproducible with some noises. The detection limit of 2-mercaptoethane sulfonic acid using this cell was 500 nM.