Non-chromatographic Speciation Analysis of Tellurium by HG-ICP-MS/MS at Sub ng L-1 Concentration in Natural Waters Using TiIII as a Pre-Reducing Agent.

Abstract

An automated and high-throughput (36 h-1) method for extremely sensitive determination of the two main tellurium species in the environment, namely, tellurite (TeIV) and tellurate (TeVI), was developed. Flow injection hydride generation was interfaced for the first time with inductively coupled plasma triple quadrupole mass spectrometry (ICP-MS/MS) detection to assure interference-free tellurium analysis. ICP-MS/MS conditions were studied in detail. Using a mixture of He + O2 gases in the reaction cell, the background signals significantly dropped and Xe isobaric interference was eliminated, allowing measurement with the most abundant Te isotopes, that is, 128Te and 130Te, and offering a huge increase in sensitivity. Volatile H2Te was selectively generated by a HCl/NaBH4 reaction from TeIV or from both TeIV and TeVI (TeIV+VI) after pre-reduction of TeVI by a TiCl3 solution. The optimum conditions for TiCl3 as a pre-reductant and the pre-reduction kinetics were also investigated. Different reduction rates were found depending on the sample stabilization media (HCl, HNO3, or EDTA). The same sensitivity was found for TeIV and TeVI, measured after pre-reduction, and no significant matrix effect was observed in both fresh and seawaters. Therefore, external calibration was used for quantification in real samples. Under optimal conditions, this method reached an unprecedented limit of detection of 0.07 ng L-1 for both TeIV and TeIV+VI and an intra-day repeatability of 5.2% at the 5 ng L-1 level. The methodology was successfully applied to the speciation analyses in commercially available certified reference materials of river water and seawater, and in bottled water and lake water samples.