Use of solid phase extraction for speciation of selenium compounds in aqueous environmental samples

The performance and optimization of an anion exchanger phase (SAX) in line with a hydrophobic phase (C18) was studied for the preconcentration of selenite [Se(iv)], selenate [Se(vi)], dimethylselenide (DMSe), dimethyldiselenide (DMDSe), diethylselenide (DESe) and diethyldiselenide (DEDSe), using a GC-MS system to characterize the different selenium species. Optimum separation and preconcentration of the inorganic selenium species were based on their retention in an SAX cartridge, with Se(iv) eluted in 25 ml of 1 mol l21 HCOOH and Se(vi) in 25 ml of 1 mol l21 HCl. Organic selenium species were retained in a C18 cartridge and eluted in 2 ml of carbon disulfide. The detection limits of the method were 1.4, 1.6, 0.6, 6.0, 400 and 900 ng l21 for Se(vi), Se(iv), DMDSe, DEDSe, DMSe and DESe, respectively, using a 1000 ml water sample, and the repeatability was less than 10%. The method was applied to natural water samples of different origins.