Adsorptive Voltammetric Study of Thorium–Alizarin Complexon Complex at a Carbon Paste Electrode

Abstract.

A new sensitive adsorptive voltammetric procedure is described for trace measurement of thorium. It is based on the cathodic stripping peak of the thorium–alizarin complexon (ALC) complex at a carbon paste electrode (CPE). The complex of Th(IV) with alizarin is adsorbed at a CPE in a mixed buffer solution (pH 5.0) which consists of 0.1 mol·L⁻¹ sodium acetate and 0.04 mol·L⁻¹ potassium biphthalate, yielding a sensitive cathodic voltammetric peak corresponding to the reduction of alizarin in the complex at −0.57 V (vs. SCE). The second-order derivative peak current of the complex is linearly dependent upon the concentration of Th(IV) over the range of 3.0×10⁻⁹ ∼8.0×10⁻⁷ mol·L⁻¹. The detection limit is 1.0×10⁻⁹ mol·L⁻¹ for 180 s accumulation. The molar ratio of each component in the complex was estimated as n_Th(IV):n_ALC=1:1 by a continuous variation method. The electrode processes of the Th(IV)–alizarin complex at a CPE were investigated. The procedure was successfully applied to the trace determination of thorium in ore and clay samples.