A new method of Sn purification and isotopic determination with a double-spike technique for geological and cosmochemical samples

Abstract

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 interferents (i.e. In, Cd and Te), as well as elements that could form molecular isobaric interferents (i.e. Ge, As, Se, Mo and Ag) with a high recovery close to 100%. The Sn isotope analysis was performed by using a Neptune Plus MC-ICP-MS equipped with jet cones. A double-spike technique was used for correcting isotope fractionation during the chemical procedure and instrumental mass bias correction and this method was shown 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 the 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 a value of 0.11‰ (2SD) was obtained. 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.