DETERMINATION OF SELENIUM IN FRESH-WATERS BY CATHODIC STRIPPING VOLTAMMETRY AFTER UV IRRADIATION

An analytical method was developed for the determination of total diss olved selenium in fresh waters, using linear sweep cathodic stripping voltammetry (CSV) in combination with UV photolytic digestion. Both th e CSV method, based on the electrodeposition and stripping of Cu2Se, a nd the UV irradiation procedure were investigated in detail. In the pr esence of dissolved organic substances, as in freshwaters, Se(VI) is r educed to Se(IV) by UV irradiation in 0.1M hydrochloric acid. Glucose can be used as the carbon source in samples low in natural dissolved o rganic carbon (DOC). The photolytic yields of Se(IV) were about 90% in both cases. Five freshwater samples were analysed For total selenium by CSV after UV photolysis, and by hydride generation atomic absorptio n spectrometry (HG-AAS) after oxidative digestion followed by reductio n with hydrochloric acid. The results agreed well and the concentratio ns were in the range 70-190 ng/l., well above the detection limit of t he CSV method at 2 ng/l.