Critical Review—Electrocatalytic Sensors for Arsenic Oxo Species

Reliable sensing of arsenic in various samples including ground waters is of importance due to its high toxicity and increasing population in the environment. Electrochemical methods have inherent features permitting selective and sensitive sensing especially in field work or in situations where more expensive and sophisticated instrumentation is not an option. A characteristic of electrochemical methods for detection and speciation of arsenic including differentiation of its oxidation states originates from the need for catalyzing various electron transfer steps particularly between As(0), As(III) and As(V). Also reduction to arsine gas and possibility of electrochemical gas sensing is an analytical option. While typical electrochemical approaches utilizing stripping or pulse voltammetry permit direct determination of arsenic(III) at the ppb levels, there is a need for the development of electrocatalytic methodology toward direct electroreduction of As(V), e.g. with use of noble metal nanoparticles (including platinum) and their alloys. Detection limits, sensitivity and selectivity can be improved by sorption and preconcentration of As on polymer gels, metal oxides or certain metals (e.g. Au, Pt, and Ag). Observations made during electrocatalytic and photoelectrochemical reductions of bromates, nitrites and carbon dioxide with use of various metal and metal oxide nanostructures can serve as guides for such research.