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Article Dans Une Revue Analytical Chemistry Année : 2019

Anion-Specific Sulfur Isotope Analysis by Liquid Chromatography Coupled to Multicollector ICPMS

Résumé

An accurate method has been developed to measure, in a single analytical run, δ 34 S in sulfite, sulfate and thio-sulfate in water samples by liquid chromatography combined with multicollector inductively coupled plasma mass spec-trometry (MC-ICPMS). The method is based on the anionic exchange separation of sulfur species prior to their online isotope ratio determination by MC-ICPMS. Mass bias correction was accomplished by a novel approach based on the addition of an internal sulfur-containing standard to the sample. This innovative approach was compared to the sample-standard bracketing procedure. On-column isotopic fractionation was observed and therefore corrected by external calibration. Isotopic ratios were calculated by linear regression slope (LRS), an advantageous method for transient signals, leading to a combined uncertainty of δ 34 S below 0.25‰ and a reproducibility below 0.5‰ for the injection of 1 µg of S. The method was successfully applied to the measurement of δ 34 S in synthetic solutions and environmental water samples. Matrix effects leading to δ 34 S overestimation were observed for sulfate in some samples with high sodium/sulfate mass ratios. The developed analytical procedure simplifies the δ 34 S analysis of liquid environmental samples since preparation steps are no longer required and allows the analysis of several sulfur-containing species in a single run. Sulfur is a key component of many natural environments, is involved in natural biogeochemical processes 1,2 and can play an important role in the biodegradation of contaminants. 3 Sulfur is highly reactive and can exist in different redox states (-II to +VI). Both reduction and oxidation of sulfur lead to large isotopic fractionation effects, which result in changes in the isotopic composition (δ 34 S) of individual sulfur species (sulfite, sulfate, thiosulfate, elemental sulfur, and tetrathionate). 4-7 Thus, measurement of the sulfur isotopic composition of specific molecules is potentially very useful for understanding the isotope fractiona-tion associated with the numerous redox reactions that characterize the modern sulfur cycle since the results combine molecular and isotopic information associated with fractionation mechanisms. The conventional approach for sulfur isotopic analysis is based on the conversion of a sample to SO2 by combustion in an elemental analyzer (EA) and determination of the 32 S/ 34 S ratio in an isotope ratio mass spectrometer (IRMS). This kind of analysis is restricted to bulk materials, and 10 to 50 µg of sulfur are needed, consequently, for water samples with low sulfur concentration, large sample volumes (> 5 L) are required. 8,9 Furthermore, the determination of δ 34 S for dissolved individual species via this method requires a tedious and time-consuming sample preparation. Isolation of each individual species can be achieved through complex and laborious steps that can lead to isotopic fractionation and contamination. Sulfate is generally recovered by precipitation with barium (Ks(BaSO4) = 1.08•10-10), but if the sample also contains sulfite, the sul-fite will also coprecipitate (Ks(BaSO3) = 5.0•
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Dates et versions

hal-02272891 , version 1 (28-08-2019)

Identifiants

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Mathieu Martinez, Jose Ignacio Garcia-Alonso, Corinne Parat, Jorge Ruiz Encinar, Isabelle Le Hécho. Anion-Specific Sulfur Isotope Analysis by Liquid Chromatography Coupled to Multicollector ICPMS. Analytical Chemistry, 2019, 91 (15), pp.10088-10094. ⟨10.1021/acs.analchem.9b02038⟩. ⟨hal-02272891⟩
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