Collaborative determination of trace element mass fractions and isotope ratios in AQUA-1 drinking water certified reference material

Arsenic in Lake Geneva (Switzerland, France): long term monitoring, and redox and methylation speciation in an As unpolluted, oligo-mesotrophic lake

Arsenic speciation was followed monthly along the spring productivity period (January-June 2021) in the Petit Lac (76 m deep) and in April and June 2021 in the Grand Lac (309.7 m deep) of Lake Geneva (Switzerland/France). Lake Geneva is presently an oligo-mesotrophic lake, and As-unpolluted. The water column never becomes anoxic but the oxygen saturation at the bottom of the Grand Lac is now below 30% owing to lack of water column mixing since 2012. Thus, this lake offers excellent conditions to study As behaviour in an unpolluted, oxic freshwater body. The following 'dissolved' As species: iAs(III), iAs(III + V), MA(III), MA(III + V), DMA(III + V), and TMAO were analysed by HG-CT-ICP-MS/MS. Water column measurements were complemented with occasional sampling in the main rivers feeding the lake and in the interstitial waters of a sediment core. The presence of MA(III) and TMAO and the predominance of iAs(V) in lake and river samples has been confirmed as well as the key role of algae in the formation of organic species. While the total 'dissolved' As concentrations showed nearly vertical profiles in the Petit Lac, As concentrations steadily increase at deeper depths in the Grand Lac due to the lack of mixing and build up in bottom waters. The evaluation of 25 years of monthly data of 'dissolved' As concentrations showed no significant temporal trends between 1997 and 2021. The observed seasonal character of the 'dissolved' As along this period coincides with a lack of seasonality in As mass inventories, pointing to a seasonal internal cycling of As species in the water column with exchanges between the 'dissolved' and 'particulate' (i.e., algae) fractions.

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

An automated and high-throughput (36 h^-1) method for extremely sensitive determination of the two main tellurium species in the environment, namely, tellurite (Te^IV) and tellurate (Te^VI), 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 Te^IV or from both Te^IV and Te^VI (Te^IV+VI) after pre-reduction of Te^VI 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 Te^IV and Te^VI, 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 Te^IV and Te^IV+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.