Anodic adsorptive stripping voltammetry at a carbon paste electrode for determination of trace thorium

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 x 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 x 10(-10) M (S/N=3), a linear current-concentration relationship is observed up to 3.0 x 10(-7) M, and the relative standard deviation is 4.2% for 15 successive determinations on the same electrode surface at the 4.0 x 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.