Determination of arsenate in natural pH seawater using a manganese-coated gold microwire electrode

作者：Gibbon Walsh Kristoff; Salauen Pascal; van den Berg Constant M G

来源：Analytica Chimica Acta, 2012, 710: 50-57.

DOI：10.1016/j.aca.2011.10.041

• Anodic stripping voltammetry
• Arsenate
• Arsenic
• Microwire electrode
• Arsenic speciation

Direct electrochemical determination of arsenate (As-V) in neutral pH waters is considered impossible due to electro-inactivity of As-V. As-III on the other hand is readily plated as As-0 on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of As-V to As-III was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to Mn-II. Advantage is taken of this redox couple to enable for the first time the electrochemical determination of As-V in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (similar to 1 mu M Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of -1.3 V. Deposition of As-0 from dissolved As-V caused elemental Mn to be re-oxidised to Mn-II in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited As-V is subsequently quantified using an ASV scan. As-III interferes and should be quantified separately at a more positive deposition potential of -0.9 V. Combined inorganic As is quantified after oxidation of As-III to As-V using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM As-V using a deposition time of 180s.

• 出版日期2012-1-13