Enhanced Cathodic Preconcentration of As(0) at Au and Pt Electrodes for Anodic Stripping Voltammetry Analysis of As(III) and As(V)

We report that the cathodic preconcentration of electron-insulating As(0) on Au and Pt electrodes can be enhanced by chemical reduction of As(III) and As(V) by electrogenerated H-2, as studied by cyclic voltammetry. This finding is used for sensitive anodic stripping voltammetry (ASV) analysis of As(III) and/or As(V) at the Au electrode. About three As(0) monolayers were cathodically preconcentrated on the Pt electrode at -0.3 V (vs SCE) in 0.5 M aqueous H2SO4, as a result of both the chemical reduction of the solution-state As(III) near the electrode surface by the electrogenerated H-2 and the direct electroreduction of As(III) on the highly catalytic surface Pt sites. Only one As(0) monolayer was electrodeposited at -0.2 V (vs SCE) on the Au electrode in 0.5 M aqueous H2SO4, but about two As(0) monolayers were deposited on the Au electrode at a more negative potential at which the mild evolution of H-2 occurred. The electrogenerated H-2 could also chemically reduce As(V), though the direct electroreduction of As(V) was sluggish on the Au electrode. Linear sweep ASV (LSASV) oxidation of the preconcentrated As(0) to As(III) and then to As(V) at a fast scan rate gave two sharper and higher anodic peaks on the Au electrode than on the Pt electrode. On the basis of these observations, sensitive dual-signal LSASV analysis of As(III) and/or As(V) was achieved on the Au electrode, with limits of detection of 1.0 nM for As(III) and 5.4 nM for As(V) under optimized experimental conditions. Our method was successfully applied for analysis of As(III) and/or As(V) in real water samples. The insights into cathodic As(0) deposition provided here may help the better understanding of electrochemical deposition of many other electron-insulating thin films, especially those obeying the electrode material-dependent inner-sphere mechanism, for electrochemical and surface-coating applications.