A new method of Sn purification and isotopic determination with double-spike technique for geological and cosmochemical samples
This study aimed at developing a new methodology for measuring tin isotope compositions in geological and cosmochemical materials. The analytical procedures included sample treatment, chemical purification and measurement protocol of Sn isotopes by mass spectrometry. A new separation protocol relying on three-stage ion-exchange chromatography was optimized. Sn was separated from matrices and isobaric interference (i.e. In, Cd and Te), as well as elements that could form molecular isobaric interferences (i.e. Ge, Ga, As, Se, Mo and Ag) with a high recovery close to 100%. The Sn isotope analysis was performed by Neptune Plus MC-ICP-MS equipped with Jet cones. A double-spike technique was used for correcting isotope fractionation during chemical procedure and instrumental mass bias correction and this method was show to provide better reproducibility. All measurements were carried out at a concentration of 10 ppb and as little as 20 ng of Sn are sufficient for a single measurement. The precision of Sn standard solution NIST SRM 3161a with double-spike method was 0.05‰ (2SD) for δ124Sn. The intermediate precision of the whole procedure was tested by measuring multiple dissolutions of several geostandards (BHVO-1, BHVO-2 and AGV-1) and gave a value of 0.11‰ (2SD). This new method has the best precision and accuracy for Sn isotope determination attained so far and has been applied to the analysis of geological and cosmochemical samples.