Speciation of arsenic(III) and arsenic(V) by manganese-mediated stripping voltammetry at gold microelectrode ensemble in neutral and basic medium

Abstract

New schemes of arsenic speciation by anodic stripping voltammetry are developed at neutral pH based on the difference in electrochemical behaviour of the As(III) and As(V) forms. Detection is performed in sulphite medium (0.1 M Na₂SO₃) in the presence of Mn(II) (10⁻⁶ M), which is known to catalyse the reduction of As(V), making it detectable by ASV. Two speciation schemes are proposed. If As(III) > As(V), then As(III) and total As(III) + As(V) are determined in separate voltammetric cells after oxidation of As(III) to As(V) (5 min ozone purging), similar to previous studies. However, when As(V) > As(III), both As(III) and As(V) can be determined consecutively, within the same cell. In this case, two simple variants were successfully tested, depending on the size of the As(III) peak in comparison to the linearity range. The working electrode is an ensemble of gold microelectrodes obtained by HAuCl₄ electrolysis at a carbon black–polyethylene composite (ratio 30:70). No purging is required, the electrode is sensitive, robust and has a long lifetime. Calculated LODs of As(III) and As(V) are 0.09 μg L⁻¹ and 0.35 μg L⁻¹, respectively (3σ, t_dep = 20 s). The proposed procedures are fast, simple and environmental-friendly.

Keywords:

• arsenic speciation
• anodic stripping voltammetry
• gold microelectrode ensemble
• manganese
• sodium sulphite

Acknowledgements

We thank Tomanalyt company (Russia) for the free access to their laboratory facilities and Metrohm (Switzerland) for the kind donation of ion exchange cartridges. We are also grateful to the referees for their extremely helpful comments.