Determining high-precision Sr–Nd isotopic ratios of certified reference materials using thermal ionization mass spectrometry

Abstract

The Thermal Ionization Mass Spectrometry (TIMS) Laboratory at CSIR-National Geophysical Research Institute, Telangana, Hyderabad, India (CSIR-NGRI) has undertaken a systematic analysis of the isotopic (Sr and Nd) compositions of the eight most frequently used certified reference materials (CRMs) used for in-house geochemical analyses. This investigation improves upon the existing database for the isotopic community. This study uses a two-step Sr–Nd separation procedure to purify Sr and Nd from the geological sample chemically digested using a modified HF–HNO₃–HCl scheme. The replicate analyses of SRM 987 and La Jolla yielded an ⁸⁷Sr/⁸⁶Sr ratio of 0.710246 ± 0.000006 (n = 8, 2SD) and an average ¹⁴³Nd/¹⁴⁴Nd ratio of 0.511844 ± 0.000008 (n = 8, 2SD) which agrees with the well-accepted value of 0.710245 ± 0.000003 and 0.511846 ± 0.000002 respectively. We report precise Sr–Nd isotopic compositions of CRMs with the 2SD of the mean of the Sr–Nd isotope analysis, always less than or equal to 10. This study presents a procedure for purifying Sr and Nd using ion exchange/extraction column chromatography. The Sr–Nd isotopic compositions of CRMs in this study match well with the published literature. We report the first precise and reliable Sr–Nd isotope data for STM-1 using ion exchange column chromatography and TIMS.