Study of electrochemical behaviour of As(III) at Au/Au and Pt/Au electrodes by electrochemical quartz crystal microbalance

In this study, the electrochemical behaviour of As(III) at Au/Au and Pt/Au electrodes was investigated with an electrochemical quartz crystal microbalance (EQCM) in Britton-Robinson buffer solutions (B-R, pH in the range 1.8–11.2) and in 0.1 or 0.5 M aqueous H2SO4. By means of real-time process monitoring the EQCM parameters (frequency etc.) and enhancing the electrode-response signals by pre-electrodeposition of As(0), we examined in detail the electrodeposition of As(0), the electrode-surface-adsorption characteristics of As(III) and As(V), and the pH-dependence of the electrochemistry of As species. The following main conclusions were reached: (1) electrodeposition of As(0) can occur on both electrodes, but electrodeposition of As(0) on Pt/Au is more significant, and the electrooxidation of As(0) electrodeposited on Pt/Au in sufficient quantities can exhibit two current peaks for oxidation of outer-layer As(0) followed by inner-layer As(0); (2) As(III) can strongly adsorb on Pt/Au but its oxidation product as As(V) can desorb from the electrode surface, and the adsorption of both As(III) and As(V) is very weak on Au/Au; (3) the electrooxidation current of As(III) on Pt/Au tends to be maximum in B-R buffer solution (pH 1.8) and in 0.1 M aqueous H2SO4. On the basis of the pre-adsorption of As(III) on Pt/Au and its catalyzed electrooxidation stripping, we proposed a new linear sweep voltammetric electroanalysis method for highly sensitive determination of As(III), by which the detection sensitivity of As(III) can be enhanced 40-fold over the pre-adsorption-free case. This study should have some reference value for in-depth understanding of the electrochemistry of arsenic and developing methods of electroanalysis of inorganic arsenic.