Determination of selenium speciation in river waters by adsorption on iron(III)-Chelex-100 resin and differential pulse cathodic stripping voltammetry

This paper describes the preconcentration of Se(IV) from polluted waters by iron(III)-loaded Chelex-100 resin and its determination by differential pulse cathodic stripping voltammetry. The method is used to study selenium speciation in waters, and a speciation method, suitable for concentration levels of environmental significance (ng/l), is defined and applied to a real polluted system (Tevere river). Besides the determination of Se(IV) and Se(VI), the method allows discrimination between “free” and “bound” dissolved Se(IV). As regards bound Se(IV), a non-labile interaction with an “unidentified species” is hypothesised and the conditional formation constant of the hypothesised process evaluated as well as the concentration of “unidentified species”. Finally, the distribution of Se(VI) and -(IV) added to untreated water samples was studied.