Anodic Adsorptive Stripping Voltammetry at a Carbon Paste Electrode for Determination of Trace Thorium

Abstract

A sensitive adsorptive stripping voltammetric procedure for trace measurement of thorium, based on the oxidation peak of thorium(IV)–alizarin complexan complex at a carbon paste electrode (CPE) during a positive-going potential scan from −0.1 V to 0.9 V (vs. SCE), is described. Optimum experiment conditions include the use of 0.12 M acetate–0.03 M potassium biphthalate buffer solution (pH4.6), 3.2 × 10−6 M alizarin complexon (ALC), an accumulation potential of −0.1 V, and a scan rate of 150 mV s−1. The detection limit after a 180 s preconcentration is 4.0 × 10−10 M (S/N=3), a linear current–concentration relationship is observed up to 3.0 × 10−7 M, and the relative standard deviation is 4.2% for 15 successive determinations on the same electrode surface at the 4.0 × 10−8 M level. Possible interferences are evaluated. The electrode processes of the adsorbed complex are proposed. The method has been applied to determination of trace thorium in ores with good results.