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The importance of selenium in the environment and in biological systems is now well recognized. Its biochemical functions, e.g., its anti-oxidant role and therefore cell protecting function, as an essential constituent of the enzyme glutathione peroxidase, has provoked a growing interest in the determination of this element. Selenoamino acids are essential for the understanding of the biogeochemical cycle of Se and TMSe+ is a known urinary metabolite present at high levels when Se is taken in excess. In this work we present a hyphenated technique (HPLC-ICP-MS) available for the separation of the organic Se compounds (selenocystine, selenomethionine and trimethylselenonium ion). The choice of column and solvents has been a critical parameter. Good repeatability and excellent detection limits (less than 1 pg 1-' for each species) have been reached for standard solutions and the application to some natural samples (enriched yeast, human serum and urine) has shown quite promising results.

Parameters for selenium determination in inductively coupled plasma mass spectrometry (ICP-MS) by pneumatic nebulization and flow injection with hydride generation (FI-HGICP-MS) have been compared. The effect of organic solvents (methanol, ethanol, propanol, acetone and acetonitrile) on the Se response has been evaluated with both sample introduction modes. Results show that the addition of alcohols leads to an important reduction of polyatomic interferences (40Ar37C1, 40Ar38Ar, 40Ar,H,) and to a 10-fold enhancement of the Se signal. The effect of the solvent on both signal enhancement and reduction of the interference mechanisms are discussed. Under optimized operating conditions (NaBH, = 0.2%, pH1, methanol load = 6%), selenium determination by FI-HGICP-MS gives detection limits (3 s,,) of 1 pg for a 200 pl sample loop with an average RSD of < 2% under routine conditions. This system has been validated by participation in a certification campaign throughout Europe for inorganic selenium. It has also been applied to the direct determination of dissolved Se'' in natural estuarine waters.