Gas chromatography-mass spectrometric characterization of SenSm compounds in synthetic melts and sediments.

A gas chromatography-mass spectrometry (GC-MS) method was used to characterize and identify mixed selenium-sulfur compounds with the formula SenSm in synthetic selenium-sulfur melts and selenium-impacted sediments. This method shows strong fragmentation of SenSm compounds in the electron ionization source, which makes conclusive identification of discrete compounds difficult. Despite these limitations, three SenSm compounds (SeS4, SeS5, and SeS6) were identified conclusively in synthetic samples, and several others were shown to be mixed SeS compounds, without being able to determine a molecular formula. Three selenium-impacted sediments from sites containing similar total selenium concentrations (11.0-18.5 ppm) were extracted with carbon disulfide (CS2); each of the three sediments contained at least 12 SenSm compounds, ten of which were common to all three sediments. Two of the compounds identified in the synthetic samples were also found in all three sediments, SeS4 and SeS5, and a third, SeS6 was found in one sediment sample. This is the first time that cyclic SenSm compounds have been confirmed to exist in the environment.

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.