Stability and Storage Problems in Selenium Speciation from Environmental Samples

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Abstract
The stability of selenite and selenate at 0.3 and 100 μg L−1 concentrations, preserved at different pH values (pH 2, 4 and 8) and stored in different containers (Teflon, polypropylene and polyethylene) at various temperatures (from −20 to 40°C) was studied for one year period. Both species were stable in acidified samples at pH 2 with HCl at −20°C in Teflon containers for the twelve months tested. However, losses of selenite were observed after 6 months in river and tap water samples. Selenate was more stable than selenite and higher concentrations were more stable than lower concentrations. The order of decreasing stability was Teflon > polyethylene > polypropylene, pH 2 > pH 4 > pH 8 and −20°C > 4°C > 25°C > 40°C. The stability of four volatile organic selenium species in seawater spiked at concentrations of 50 μg L−1 for both DMSe and DESe and at concentrations of 0.50 μg L−1 for both DMDSe and DEDSe, stored at two temperatures (4°C and −20°C) in three different container materials (Teflon, polyethylene and polystyrene) was studied. The four species were only stable for 24 h. The order of decreasing stability was DMDSe > DESe > DEDSe > DMSe, Teflon > polyethylene > polystyrene and −20°C > 4°C.