LAUSR

Selenosulfate (SeSO32-) has been shown to occur in certain industrial process waters, and selenopolythionates (SenSxO62-) can be suspected to form from SeSO32- via oxidative or addition reactions. We report here the first observation of selenopolythionates in waters by mass spectrometry. The high mass accuracy and ultra-high resolution of Fourier transform-ion cyclotron resonance-mass Spectrometry with electrospray ionization (ESI-FT-ICR-MS) were used to analyze the isotope patterns of selenium (Se), sulfur (S), and oxygen (O) satellites, in order to provide unequivocal determination of the molecular sum formula of three different selenopolythionates. An aged aqueous solution of SeSO32- was shown to contain the sodium adducts of selenotrithionate (NaSeS2O6-), diselenotetrathionate (NaSe2S2O6-), and triselenopentathionate (NaSe3S2O6-). The identity of these ions was confirmed by accurate mass determination (Δ m/z < 3 ppm error) and by isotopic intensity ratio analysis of the [MIS+2] satellites. Furthermore, Collision Induced Dissociation (CID) was applied to selenotrithionate to distinguish between isomers, and the fragmentation mass spectrum reveals that the Se atom in NaSeS2O6- is located in the middle of the chalcogen chain. Ion chromatographic analysis of the analyzed selenosulfate solutions indicates that selenopolythionates are not suitable for determination by common separations employed for Se speciation analysis, which emphasizes the value of ESI-FT-ICR-MS for complete qualitative characterization of trace element speciation in solution.