Voltammetric determination of inorganic As(III) and total inorganic As in natural waters.

The paper describes a voltammetric method for the determination of As(III) and total inorganic As at ppb and sub ppb level using cathodic stripping voltammetry. This method is based on the formation of a copper-arsenic intermetallic at HDME during the preconcentration step. Sodium dithionite is used for the reduction of As(V) to As(III). As(III) is then determined in HBr supporting electrolyte. Compared to the procedures described in previous literature, the determination of total inorganic arsenic in such conditions needs shorter deposition times and less amount of copper. Moreover, better linear response current versus concentration and peaks repeatability are obtained. In the described working conditions LOQ for As(III) and As(V) are 0.010 and 0.020 ppb respectively, for a deposition time of 300 s. Standard deviation for 1 ppb arsenic concentration (n = 7) is 5%. The method was applied to thermal, spring and sea waters and accuracy was verified by a recovery test on spiked samples. Total arsenic concentrations are in good agreement with those obtained in ICP-OES-HG.