EFFECT OF PHYSICOCHEMICAL PARAMETERS ON TRACE INORGANIC SELENIUM STABILITY

The stability of Se(IV) and Se(VI) species at 10 and 50 ng ml(-1) conc entrations, at different pH values, in the presence or absence of chlo ride and stored at different temperatures and in different containers was reported. Se(IV) was determined by hydride generation atomic absor ption spectrometry (HG-AAS) and Se(VI) by reducing Se(VI) to Se(IV) an d calculating the difference between total inorganic Se and Se(IV). Ne utron activation analysis (NAA) was used for quality control. Complete loss of Se(IV) occurred after twelve months when samples were stored in polyethylene containers at pH 2 in the absence and in the presence of chloride. Se(VI) was stable under those conditions fos the twelve m onths tested. The stability of Se(IV) increased at pH 6, with two mont hs being the maximum storage time without risk of Se(IV) loss. The pre sence of Cl- decreased the risk of losses in some cases. PTFE containe rs increased Se(IV) losses at pH 6, especially at 10 ng ml(-1). Both s pecies were stable at -20 degrees C for the twelve months tested and l osses of Se(IV) and Se(VI) were lower at 40 degrees C than at room tem perature. A discussion of these results and data published in the lite rature are included in this paper.