Gas chromatography-mass spectrometric characterization of Se_nS_m 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 Se_nS_m in synthetic selenium-sulfur melts and selenium-impacted sediments. This method shows strong fragmentation of Se_nS_m compounds in the electron ionization source, which makes conclusive identification of discrete compounds difficult. Despite these limitations, three Se_nS_m 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 Se_nS_m 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 Se_nS_m compounds have been confirmed to exist in the environment.