CATHODIC STRIPPING POTENTIOMETRIC DETERMINATION OF SELENIUM IN BIOLOGICAL AND ENVIRONMENTAL MATERIALS

The use of cathodic stripping potentiometry for the reliable determination of trace and ultra trace concentrations of selenium in environmental and biological samples on a glassy carbon mercury film electrode is described. The optimum conditions for the method include 3 M HCl as supporting electrolyte, an electrolysis potential of - 100 mV vs. SCE, a constant reduction current of -20 CLA and the decomposition of the samples by dry ashing with magnesium nitrate as an ashing aid. Under these conditions, the detection limit is 0.8 mu g/l with an electrolysis time of 5 min or 0.04 mu g/l with 60 min deposition. The relative standard deviation for the measurement at this level is 6% (n = 7). The presence of inorganic and organic substances such as lead, copper, cadmium, zinc, CTMAB, LAS, LPC and Triton X-100 caused some suppression of the selenium peak, but these effects were easily circumvented by the use of standard additions method and a UV-irradiation procedure. The W-irradiation of the digested environmental and biological materials was also effective in reducing the required dry ashing period to 1 h, as well as in improving the sensitivity and accuracy of the method.