Abstract

A study was carried out to evaluate the analytical capabilities of coupling chemical bromide generation with inductively coupled plasma atomic emission spectrometry for the determination of selenium in both oxidation states, VI and IV. The method is based on the generation of two volatiles of selenium(VI) and (IV) by reaction with bromide ions in sulfuric acid media in a discontinuous mode and transport of the gaseous phase to the plasma torch. After evaluation of the main and interactive effects of the experimental variables by experimental design the three most influential variables were optimized for each determination by the modified Simplex method. The volatilization efficiency of both volatile species was determined. The mean of six experiments gave volatilization efficiencies of 73 and 77% for Se^VI and Se^IV, respectively. Under the optimized analytical conditions selenium can be determined after volatilization of Se^VI with an absolute detection limit (3s) of 0.25 ng for the injection of 200 µl of the sample solution. The precision (RSD) was 2% for the injection of five replicates of 2.0 ng of Se^VI (200 µl of a 0.1 µg ml⁻¹ solution). Again under optimized conditions for Se^IV, like Se^VI, an absolute detection limit for selenium of 0.31 ng with a reproducibility (RSD) of 6.8% was obtained. The interference of common anions and cations on the selenium signal of both states (VI and IV) was evaluated. The Se^VI method was applied to the determination of selenium in cosmetic gel shampoos and the method for Se^IV was applied to the determination of selenium in dietetic compounds. The results were validated in both cases by using alternative methods.