Extraction and determination of elemental selenium in sediments—A comparative study

This paper proposes a new technique to extract elemental Se from soil and sediment samples. In this study, we have identified that the purchased red elemental selenium standard (PF-Se) was impure and rather consisted of a mixture of CS2 soluble amorphous elemental Se (ca. 10%, w/w), water soluble oxidized Se (ca. 15–17%, w/w) and, CS2 insoluble red monoclinic elemental Se. In more recent studies, a slow oxidation and a mineral phase transition of this sample was also observed. The solubility of the amorphous elemental Se in CS2 was at least 0.64 mg L−1. The black elemental Se purchased from Sigma–Aldrich had a much lower solubility in CS2 (7.2 μg mL−1) compared to that given in the literature. Any selenium compounds with electrical charge and polar nature is insoluble in CS2. In a sodium sulphite solution, PF-Se was completely dissolved thus giving a clear indication of the lack of selectivity in that extraction system. Other comparative studies also demonstrated that over extraction did occur with the Na2SO3 method. Compared to Na2SO3, CS2 extraction of elemental Se is not only much simpler, straightforward and with higher analytical precision, but also much more selective and accurate. With HG-AFS, the detection limit can reach as low as 1.0 ng g−1 in sediment sample owing to a low reagent blank of CS2 solvent.