Reverse phase ion pair chromatography coupled with inductively coupled plasma mass spectrometry as a method for tungsten speciation in natural waters

In the past 20 years, the occurrence of tungsten-related health and safety incidents has drawn the close attention of scholars to the toxicity of tungsten and its health and environmental effects. The upper limit of tungsten concentration in water, its mobility and toxicity are all closely related to its speciation. Although polytungstates have been proven to be more toxic and migratory than monomeric tungstates, there is limited information about their abundance in natural environments due to the lack of a reliable analytical approach for determination. In this study, we conducted a simultaneous analysis of monomeric and polymeric tungsten species in natural water using reverse-phase ion pair chromatography coupled with inductively coupled plasma mass spectrometry. Polytungstates and five monotungstates, including tungstate as well as mono, di, tri, and tetrathiotungstate, were chromatographically separated within 35 min of using ethanol (12 - 48% gradient) as the mobile phase. The detection limit of polytungstates was 1.50 µg/L. Although common for the analysis of metals, experimental studies based on electrospray ionization - high resolution mass spectrometry (ESI-HRMS) have indicated that samples containing polytungstates should not be acidified, as it could result in the transformation of monotungstates to artifact polytungstates. Overall, our study offers an effective method for the analysis of various tungsten species, especially polytungstates, at environmentally relevant concentrations.