Speciation of Inorganic Arsenic in Natural Waters by Square-Wave Cathodic Stripping Voltammetry

Abstract

A fast and sensitive voltammetric method for the determination of arsenite and total inorganic arsenic in natural water systems is described using square-wave cathodic stripping voltammetry at a hanging mercury drop electrode. All the determinations were done in 1 M HCl, in the presence of 5 ppm copper(II) and dissolved oxygen. Discrimination between both oxidation states is achieved just by varying the composition of the supporting electrolyte: reduction of As(V) to As(III) is carried out at room temperature by a mixture of potassium iodide and ascorbic acid and inorganic arsenic determined as As(III)+As(V), while As(III) is measured in the absence of the reducing agent. For an accumulation time of 60 s the detection limits were 0.7 ppb for As(III) in 1 M HCl, and 5 ppm Cu(II), 0.6 ppb for As(III)+As(V) in 1 M HCl, 5 ppm Cu(II) and 0.04 % (w/v) KI+0.02 % (w/v) ascorbic acid. The precision, expressed as relative standard deviation (RSD) at 95 % confidence level, was calculated as 9 % from ten individual measurements taken at 2 ppb standard. The method was tested by the measurement of As(V) and As(III) in real and synthetic natural water samples.