Speciation analysis of selenium using voltammetric techniques

A simple and accurate method for the separation and determination of Se(IV), selenocystine and dimeihyldiselenide has been developed based on differential pulse cathodic stripping voltammetry (DPCSV) at a hanging mercury drop electrode (HMDE) and an extraction procedure for the prior separation of the Se species. Thus, selenocystine and Se(IV) were determined simultaneously in the aqueous phase using HCl as electrolyte, while the determination of dimethyldiselenide was achieved in the organic phase after extraction of the sample with dichloromethane using as electrolyte LiClO4 in absolute ethanol acidified with HCl. No significant effect on the determination of selenocystine by the presence of sulfur-cystine, even in a 300-fold greater concentration, was observed. For the optimization of the procedure several parameters of the voltammetric determination, such as the deposition time and voltage, the kind of electrolyte and the acidity of the sample as well as the kind of extractant for the effective separation of the Se species were investigated in the aqueous and organic phase. Moreover, the quantitatively transformation of the electrochemically inactive Se(VI) to Se(II) was achieved by testing different reducing agents. The capability of the developed procedure was tested on the SRM 1633a (coal fly ash) reference material and the whole procedure was applied on a soil sample of Thermopyles Spa (Greece). (C) 2002 Elsevier Science B.V. All rights reserved.