A simple and reliable anion exchange resin method for sulfate extraction and purification suitable for multiple O- and S- isotope measurements.
Résumé
Rationale:
The O- and S- isotope compositions of sulfates can be used as key tracers of the fate and sink of sulfate in both terrestrial and extra-terrestrial environments. However, their application remains limited in those geological systems where sulfate occurs in low concentrations. Here we present a simple and reliable method to extract, purify and concentrate sulfate from natural samples. The method allows us to take into account the separation of nitrate, which is known to be an issue in O-isotope analysis.
Methods:
The separation and concentration of sulfate from other anions in any aqueous solution are performed within a few hours via anion exchange resin. The possible O- (δ18O and Δ17O) and S- (δ34S, Δ33S and Δ36S) isotope exchanges, fractionations and/or contaminations are for the first time monitored during the whole procedure using initial O- and S-mass-dependent and mass-independent sulfate solutions.
Results:
After elution in HCl, pure sulfate is fully retrieved and precipitated into BaSO4, which is suitable for O- and S- isotopic measurements using established techniques. The analysis of retrieved barite presents no variation within 2σ uncertainties: ± 0.5‰ and ± 0.1‰ in O (δ18O, Δ17O) and ± 0.2‰, ± 0.02‰ and ± 0.09‰ in S (δ34S, Δ33S and Δ36S) isotope ratios, respectively.
Conclusions:
This study shows for the first time that the resin method for sulfate extraction and purification, in addition to being cheap, simple and quick, is applicable for the measurements of all O- and S-isotopic ratios in sulfates (including the Δ17O, Δ33S and Δ36S values). Therefore, this method can be easily used for a high range of natural samples in which sulfate occurs in low concentration including aerosols, ice cores, sediments, volcanic deposits, (paleo)soils and rainwater and it can thus be a key to our understanding of the sulfur cycle on Earth.