An Analysis Method of Thiotungstates in Natural Water

Analysis of thiotungstates in natural water is of great importance for systematically investigating the environmental geochemistry of tungsten. In this paper, a method based on a system combining reversed-phase ion pair chromatography and inductively coupled plasma mass spectrometry is proposed to simultaneously determine the concentrations of tungstate (WO₄^2‒) and four thiotungstates (including WO₃S^2‒, WO₂S₂^2‒, WOS₃^2‒ and WS₄^2‒). The speciation analyses of these five tungsten compounds were performed by a high-resolution electrospray ionization mass spectrometer. Sulfide-rich geothermal water samples were snap frozen at -20 ℃ and transported to the laboratory. After thawing under anaerobic conditions, the five tungsten compounds were separated and determined within 30 min using optimized chromatographic and mass spectrometric conditions. The working curves were established using tungstate as the standards for the other tungsten compounds, with good linear relation (correlation coefficient R² > 0.999) in the concentration range of 0.001-20 mg/L. The limits of detection (LOD) for tungstate, monothiotungstate, dithiotungstate, trithiotungstate and tetrathiotungstate were 0.82 µg/L, 0.34 µg/L, 0.22 µg/L, 0.79 µg/L and 0.62 µg/L, respectively. This method has the advantages of high sensitivity and good reproducibility, and provides an effective way for the detection and research of thiotungstates in natural water.