OPTIMIZATION OF THE DIFFERENTIAL-PULSE CATHODIC STRIPPING VOLTAMMETRYANALYTICAL METHOD FOR THE SPECIATION OF INORGANIC SELENIUM

This paper describes an optimization of the differential pulse cathodi c stripping voltammetry analytical method (DPCSV) used for selenium tr ace determination. The influence of the different electrochemical para meters as well as of the nature of the supporting electrolyte were stu died. In optimized electrochemical conditions, H2SO4 (0.1 mol l(-1)) g ives the lower Se(IV) detection limit (25 ng l(-1)). A study of interf erences brought by natural water salinity on Se(IV) detection by DPCSV was carried out and no disturbance was observed. On the other hand, t he presence of fulvic acids strongly hinders Se(IV) measurements and t he detection limit can reach 750 ng l(-1) if fulvic acids are present at a 5 mg l(-1) concentration. This DPCSV method has been used to deve lop a selenium speciation scheme based on different physico-chemical p retreatments of samples followed by the determination of Se(IV). This scheme was applied to Se speciation of synthetic and natural waters sp iked with the following selenium species: Se(IV), Se(VI) and selenomet hionine. Satisfactory results were obtained. The control of the DPCSV method and of the different pretreatments was realised by determining total selenium in a white clover certified reference material. The goo d agreement with certified values validates these methods.