Kris Latruwe

Experimental study of mass-independence of Hg isotope fractionation during photodecomposition of dissolved methylmercury

Experiments modelling photolytic decomposition of methylmercury chloride in aqueous solutions of different chemical composition have been performed. Ion-exchange chromatographic separation using Chelex® 100 resin was used in order to separate methylmercury from inorganic mercury prior to the isotope ratio measurements by solution nebulization multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The performance of the chromatographic separation has been evaluated in terms of recovery of both methylmercury and inorganic Hg using synthetic solutions. Both mass-dependent and mass-independent fractionation of Hg isotopes concomitant with the decomposition process have been observed. Mass-independent Hg isotope fractionation (MIF) resulted in selective enrichment of 199Hg and 201Hg relative to the other isotopes in the methylmercury molecules and has been attributed to the magnetic isotope effect. The highest extent of MIF of Hg isotopes, expressed as Δ199Hg and Δ201Hg values, has been observed in acidified solution with low concentration of total dissolved solids (TDS). Progressive decrease in Δ199Hg and Δ201Hg values in acidified solution with higher concentration of TDS, alkaline solutions of both low and high concentration of TDS, and in a solution of ascorbic acid has been attributed to suppression of the radical pair reaction mechanism, responsible for the occurrence of the magnetic isotope effect, by substances acting as radical scavengers, such as OH− or ascorbic acid. The data obtained in this study demonstrate the significance of spin chemistry effects in the isotope fractionation of mercury.

The Sr–Nd isolation procedure for subsequent isotopic analysis using multi-collector ICP-mass spectrometry in the context of provenance studies on archaeological glass

Sr and Nd isotopic analysis of glass can be relied upon to unravel the provenance of the flux component and the sand used in the manufacturing of archaeological glasses, respectively. For a reliable isotopic analysis of the target elements using multi-collector ICP-mass spectrometry, the target elements need to be isolated from the matrix to permit adequate correction for instrumental mass discrimination. In this paper, a simple, fast and reliable analytical method for the isolation of Sr and Nd from complex sample matrixes such as archaeological glasses is proposed. Special attention is focused on the Nd isolation protocol, with the definition of TRU-Spec and Ln-Spec resin bed volumes and of an appropriate HCl concentration to optimize Nd elution from the column.

Lead isotopic analysis of Antarctic snow using multi-collector ICP-mass spectrometry

Reliable determination of Pb isotope ratios in Antarctic snow is challenging because of the low analyte concentration and the low volume of sample typically available. In this work, a combination of a total sample consumption introduction system (the torch-integrated sample introduction system, TISIS) with multi-collector ICP-mass spectrometry (MC-ICP-MS) was used for this purpose. With this instrumental setup, accurate and precise determination of Pb isotope ratios was possible at concentrations as low as 0.5 ng mL−1, while using 0.2 mL of solution only (total amount of Pb: 100 pg). At 10 ng mL−1, the repeatability for the 207Pb/206Pb ratio was 0.16‰ RSD. The concentration range was further extended downwards by using 100-fold analyte element preconcentration via freeze-drying of 20 g of snow. The Pb concentration in procedural blanks was 0.5 ± 0.3 pg g−1, enabling the determination of Pb isotope ratios in snow samples containing down to 5 pg g−1 of Pb. After development and validation, the procedure was applied to snow samples collected at Dome C (East Antarctic Plateau) on a monthly basis during the 2006 and 2010 campaigns. The method developed was able to reveal a seasonal variation in the Pb isotope ratios occurring during 2006 and strong inter-annual variation between the two campaigns.

Determination of the isotopic composition of sub-ng amounts of Sr in Antarctic snow by multi-collector ICP-mass spectrometry

Determination of the 87Sr/86Sr isotope ratio in Antarctic snow can provide useful information on the sources of the atmospheric particulates in present and ancient times. However, precise and accurate determination of the 87Sr/86Sr ratio is challenging because of the low analyte concentration and the limited amount of sample typically available. In this work, Sr was first pre-concentrated 30-fold via evaporation, after which Sr was chromatographically isolated from the matrix (and thus separated from Rb, avoiding isobaric overlap of 87Sr and 87Rb). Subsequently, the sensitivity of the multi-collector ICP-mass spectrometer was maximized by using an Aridus II membrane desolvating system, a high-transmission interface and 1012 Ω amplifiers instead of the standard 1011 Ω ones. With this instrumental setup, the repeatability for 87Sr/86Sr ratio measurements was 0.3 and 0.5‰ RSD at 0.8 ng mL−1 (or for 320 pg in the 0.4 mL of sample solution consumed) and at 0.4 ng mL−1 (or for 160 pg) of Sr, respectively. The procedural blank was 2.5 ± 0.5 pg and did not significantly affect the 87Sr/86Sr ratio measured using 160 pg of analyte (at 0.4 ng mL−1). The accuracy of the procedure was evaluated via replicate analysis of NIST SRM 987 SrCO3 isotopic reference material. The experimental data agreed with the accepted value within the experimental uncertainty both at 0.8 ng mL−1 (for 320 pg) and at 0.4 ng mL−1 (for 160 pg) of Sr. The method was applied to the analysis of Antarctic snow samples (30 g) containing 0.5–2.1 ng of Sr. The precision was fit for the purpose of discriminating between potential source areas (PSAs). The entire procedure required ∼30 g of snow per sample, potentially enabling the contributions of PSAs to be unravelled with high temporal resolution.