Electrochemical detection of As3+ and As5+ by anodic stripping voltammetry at a gold electrode

In this article, electrochemical detection of arsenite (As3+) and arsenate (As5+) by stripping voltammetry at a gold electrode has been investigated. As3+ and As5+ are reduced to arsine (AsH3) in 0.1 M sodium borohydride before deposition on the electrode surface. 0.1 M HCl was used as the supporting electrolyte, where Cl-ions act as an ionic bridge, facilitating reduction at the working electrode. As3+ and As5+ can be deposited as arsine by simple electrochemical reduction at -0.5 V (versus Ag/AgCl). Anodic stripping voltammograms of arsine at a gold electrode showed similar peak potentials for As-0 oxidation (approximate to 0.31 V versus Ag/AgCl) under the optimum conditions (deposition potential, deposition time, and scan rate of -0.5 V, 60 s, and 200 mV/s, respectively). The stripping voltammograms for As3+ and As5+ presented similar peak shapes and current intensities. A reaction mechanism involving reduction to As-0 at a mild potential in a strong acid, followed by oxidation of As-0 to As3+ at the gold electrode, was proposed. The method developed offers a wide linear concentration range for As3+ (0-5 ppm) and As5+ (0-20 ppm) and very low limits of detection for As3+ (0.85 ppm) and As5+ (6.07 ppm).