Optimization of LC-DRC-ICP-MS for the speciation of selenotrisulfides with simultaneous detection of sulfur and selenium as oxides combined with determination of elemental and isotope ratios

Abstract

A LC-DRC-ICP-MS method for the simultaneous detection of selenium and sulfur in the selenotrisulfides selenocysteineglutathione (Cys-Se-SG) and selenodiglutathione (GS-Se-SG) is described. Both sulfur and selenium are reacted with oxygen in the dynamic reaction cell (DRC) and detected as oxides. The selenotrisulfides were separated applying a 30 min gradient liquid chromatographic (LC) method with a formic acid/methanol eluent. The detection limits for sulfur (as ³²S¹⁶O⁺) and selenium (as ⁸⁰Se¹⁶O⁺) in the chromatographic system were 4.0 and 0.2 μg L⁻¹ (100 and 5 ng in absolute mass units), respectively. S/Se elemental ratios in the 1.9–2.1 range, close to the theoretical value of 2.0, was found for both selenotrisulfides along with accurate (<2.5% deviation) and precise (∼1% RSD) sulfur and selenium isotope ratios. This emphasises the potential of the developed method for the speciation of sulfur and/or selenium compounds combined with measurement of elemental and isotope ratios in the characterisation and quantification of biomolecules and drug metabolites.