Determination of Se8 in sediments by gas chromatography-mass spectrometry.

A gas chromatography-mass spectrometry (GC-MS) method was developed to analyze cyclooctaselenium (Se8) in sediments after extraction with carbon disulfide (CS2). The method suffers from some analytical complications, most notably a poor peak shape for Se8, manifesting in a broad peak (2 min) with strong fronting, and a decrease in Se8 retention time with decreasing concentration. Detailed analysis of the mass spectral data suggests that (thermal) decomposition of Se8 on the GC column is responsible for both of these phenomena. Despite these limitations, GC-MS with selected ion monitoring (SIM) yielded a sufficiently low detection limit, 10 µg/kg (dw), to analyze Se8 in selenium-impacted sediments. The CS2 extraction appears to be selective enough to allow the determination of Se8 in sediments without further cleanup when GC-SIM-MS is used for analysis. One selenium-impacted sediment contained 7.1 mg/kg (dw) Se8, corresponding to 41% of its total selenium and as much as 50% of its total elemental selenium. This is the first time that Se8 has been positively identified in the environment. Preliminary results also indicated the presence of mixed Se-S rings in this sediment.