Storage of aqueous solutions of selenium for speciation at trace level

Different studies carried out in recent years on the preservation of trace selenium species in aqueous solutions are reviewed and experimental results showing a 29% oxidation of Se(IV) to Se(VI) in less than one month in acidic and oxygenated medium in the presence of chloride ions are presented. The hypothesis of an oxidation of Se(IV) to Se(VI) at acidic pH by traces of Cl2, obtained by a reaction between chloride ions and dissolved oxygen, followed by chlorine oxidation, is examined.