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

• Published in: Analytica chimica acta Vol. 710; pp. 50 - 57
• Main Authors: Gibbon-Walsh, Kristoff, Salaün, Pascal, van den Berg, Constant M.G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 13-01-2012; Elsevier
• Subjects: Analytical chemistry; Anodic stripping voltammetry; Arsenate; Arsenates - analysis; Arsenic; Arsenic speciation; Chemistry; Electrochemical methods; Electrochemical Techniques; Electrodes; Exact sciences and technology; Gold - chemistry; Hydrogen-Ion Concentration; Manganese - chemistry; Microwire electrode; Oxidation-Reduction; Salinity; Seawater - chemistry; Water Pollutants, Chemical - analysis; Arsenic speciation; Microwire electrode; Arsenic; Arsenate; Anodic stripping voltammetry; Gold; Arsenates; Electrochemical method; Coatings; Direct method; Reduction; Sensitivity; Redox couple; Detection limit; Hypochlorites; Reaction mechanism; pH; Oxidation; Deposition; Electrode potential; Speciation; Seawater; Manganese
• DOI: 10.1016/j.aca.2011.10.041
• EISSN: 1873-4324
• ISSN: 0003-2670

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► Determination of arsenic(V) in water of neutral pH. ► An unusual redox couple of elemental Mn/As
V reduces As
V to As
III. ► Novel manganese coated gold microwire electrode.
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 (∼1
μM 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 180
s.