An Analytical Method for Quantification of Sn Isotope Variations in Geological Materials Using MC‐ICP‐MS

Abstract

A robust analytical method is presented here, for measurements of Sn isotope variations with high precision using a multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS). A silicate rock dissolution procedure was used, together with means to remove organic matter introduced by the resin during ion‐exchange chromatography. The two‐stage ion exchange chromatography efficiently isolates Sn from the matrix and isobarically interfering elements, from samples with variable Sn mass fractions (~ 0.03 to 7 μg g−1). A double spike technique was also implemented to correct any secondary mass bias induced during sample processing and isotope ratio measurements. An intermediate precision (2s) of ± 0.47 was obtained for ε122/118Sn (using internal normalisation; n = 70 over a period of 29 months), ± 0.021‰ for δ122/118Sn (using double spike; n = 176 over a period of 29 months) and ± 0.059‰ for δ122/118Sn (using Sb doping; n = 34 over a period of 4.5 months) for the Sn standard solution, NIST SRM 3161a (Lot# 140917). The δ122/118SnNIST SRM 3161a of eleven geological reference materials are reported for the first time (BIR‐1a, BRP‐1, DTS‐2b, ECRM 782‐1, JP‐1, OKUM, QLO‐1a, RGM‐2, SGR‐1b, STM‐2 and UB‐N), with five others (AGV‐2, BCR‐2, BHVO‐2, GSP‐2 and W‐2a) showing similar results to previous studies, generally with improved precision. The intermediate precision (2s) of replicate dissolutions of ten RMs (AGV‐2, BCR‐2, BHVO‐2, BIR‐1a, DTS‐2b, GSP‐2, OKUM, SGR‐1b, STM‐2 and W‐2a) varied from 0.003 to 0.054‰. Typical repeatability precision (2SE) of individual measurements of these ten RMs over multiple measurement sessions varied from 0.031 to 0.297‰ (with 120Sn+ beam intensity < 2.37 V) and 0.017 to 0.025‰ (with 120Sn+ beam intensity > 2.37 V).