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Voltammetric detection of As(V) in natural waters

Arsenic is ubiquitous in the environment, with its sources being of natural and anthropogenic origin. It is classified as a group 1 human carcinogen by the International Agency for Research on Cancer (IARC Monographs, 1980), which makes monitoring the environmental levels of arsenic very important. The concentrations of arsenic in freshwater range from 1 to 130 nM and in seawater from 1 to 30 nM, and can be up to μM level in contaminated groundwater. Threshold values for arsenic in drinking water, proposed by the World Health Organisation, are around 130 nM (1μg/L). Arsenic in the aquatic systems is present mainly in the form of inorganic trivalent arsenite species and pentavalent arsenate oxyanions. As(III) species are considered 60 times more toxic then the pentavalent species. There are reported voltammetric techniques for As(III) environmental sensing (Touilloux et al., 2015). Voltammetry enables the development of robust low cost sensors that can be adapted for in-situ measurements, making them especially attractive for environmental monitoring. Voltammetric detection of As(V) is limited to working at pH values below 2 (Gibbon-Walsh et al., 2010). An acidification step significantly complicates the development of an electrochemical sensor probe for in situ monitoring, and makes such tools difficult to use in arsenic speciation analysis. In the work by Zhang et al. (2009), a polymer composed of aniline and o-aminophenol (PANOA), has been shown to electrocatalyze the reduction of As(V) in the process of arsenate removal. PANOA was shown to be electroactive in the pH range from 5.6 to 7. This idea was implemented into development of a PANOA modified gold microelectrode for As(V) detection. By using square wave anodic stripping voltammetry, As(V) can be measured after it has been reduced to As(III) at the PANOA-sensor surface vicinity. This work presents the preliminary research conducted on voltammetric detection of As(V) at pH 6. The ultimate aim is to obtain a sensor enabling direct As(V) monitoring at (sub-) nanomolar concentrations in close-to-neutral pH aquatic systems. REFERENCES: IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. 1980: Some Metals and Metallic Compounds, 23. Touilloux, R., Tercier-Waeber, M.-L. & Bakker, E. 2015: Antifouling membrane integrated renewable gold microelectrode for in situ detection of As(III), Analytical Methods, 7, 7503-7510. Gibbon-Walsh, K., Salaün, P. & Van den Berg, C. 2010: Arsenic speciation in natural waters by cathodic stripping voltammetry, Analytica Chimica Acta, 662(1), 1-8. Zhang, Y., Li, Q., Sun, L. & Zhai, J. J. 2009: The electrocatalytic reduction and removal of arsenate by poly(aniline-co-o- aminophenol), Electroanalytical Chemistry, 636, 47-52.

arsenic; voltammetry; polymer; gold microelectrode

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