ANALYTICAL METHODS FOR THE SPECIATION OF SELENIUM-COMPOUNDS - A REVIEW

Selenium, like sulphur, exists in the environment in several oxidation states and as a variety of inorganic and organic compounds. Dissolved inorganic selenium can be found in natural waters as selenide Se (-II), as colloidal elemental selenium Se (0), as selenite anions HSeO3- and SeO32- i.e. Se (+IV) and as the selenate anion (SeO42-) i.e. Se (+VI). Organic forms of selenium that may be found in organisms, air or in the aqueous environment, are volatile (methylselenides) or non volatile (trimethylselenonium ion, selenoamino acids and their derivatives). Knowledge of the different chemical forms and their environmental and biomedical distribution is important because of the dependence of bioavailability and toxicity on speciation. This paper reviews the different analytical methods used for the speciation of selenium compounds, with special attention to inorganic selenium and organoselenium species.