Determination of radiogenic and stable strontium isotope ratios (87Sr/86Sr; δ88/86Sr) by thermal ionization mass spectrometry applying an 87Sr/84Sr double spike

Abstract

Recent findings of natural strontium isotope fractionation have opened up a new field of research in non-traditional stable isotope geochemistry. While previous studies were based on data obtained by MC-ICP-MS we here present a novel approach combining thermal ionization mass spectrometry (TIMS) with the use of an ⁸⁷Sr/⁸⁴Sr double spike (DS). Our results for the IAPSO sea water and JCp-1 coral standards, respectively, are in accord with previously published data. The strontium isotope composition of the IAPSO sea water standard was determined as δ^88/86Sr = 0.386(5)‰ (δ values relative to the SRM987), ⁸⁷Sr/⁸⁶Sr* = 0.709312(9) n = 10 and a corresponding conventionally normalized ⁸⁷Sr/⁸⁶Sr = 0.709168(7) (all uncertainties 2SEM). For the JCp-1 coral standard we obtained δ^88/86Sr = 0.197(8)‰, ⁸⁷Sr/⁸⁶Sr* = 0.709237(2) and ⁸⁷Sr/⁸⁶Sr = 0.709164(5) n = 3. We show that by applying this DS-TIMS method the precision is improved by at least a factor of 2–3 when compared to MC-ICP-MS.