Stability and storage problems in selenium speciation from environmental samples

The stability of selenite and selenate at 0.3 and 100 mu g L-1 concentratio ns, preserved at different pH values (pH 2, 4 and 8) and stored in differen t containers (Teflon, polypropylene and polyethylene) at various temperatur es (from -20 to 40 degrees C) was studied for one year period. Both species were stable in acidified samples at pH 2 with HCl at -20 degrees C in Tefl on containers for the twelve months tested. However, losses of selenite wer e 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 > polyethylen e > polypropylene, pH 2 > pH 4 > pH 8 and -20 degrees C > 4 degrees C > 25 degrees C > 40 degrees C. The stability of four volatile organic selenium s pecies in seawater spiked at concentrations of 50 mu g L-1 for both DMSe an d DESe and at concentrations of 0.50 mu g L-1 for both DMDSe and DEDSe, sto red at two temperatures (4 degrees C and -20 degrees 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 -2 0 degrees C > 4 degrees C.