High‐Precision Measurement of Stable Cr Isotopes in Geological Reference Materials by a Double‐Spike TIMS Method

Abstract

Chromium (Cr) isotopes have been widely used in various fields of Earth and planetary sciences. However, high‐precision measurements of Cr stable isotope ratios are still challenged by difficulties in purifying Cr and organic matter interference from resin using double‐spike thermal ionisation mass spectrometry. In this study, an improved and easily operated two‐column chemical separation procedure using AG50W‐X12 (200–400 mesh) resin is introduced. This resin has a higher cross‐linking density than AG50W‐X8, and this higher density generates better separation efficiency and higher saturation. Organic matter from the resin is a common cause of inhibition of the emission of Cr during analysis by TIMS. Here, perchloric and nitric acids were utilised to eliminate organic matter interference. The Cr isotope ratios of samples with lower Cr contents could be measured precisely by TIMS. The long‐term intermediate measurement precision of δ53/52CrNIST SRM 979 for BHVO‐2 is better than ± 0.031‰ (2s) over one year. Replicated digestions and measurements of geological reference materials (OKUM, MUH‐1, JP‐1, BHVO‐1, BHVO‐2, AGV‐2 and GSP‐2) yield δ53/52CrNIST SRM 979 results ranging from −0.129‰ to −0.032‰. The Cr isotope ratios of geological reference materials are consistent with the δ53/52CrNIST SRM 979 values reported by previous studies, and the measurement uncertainty (± 0.031‰, 2s) is significantly improved.

Tracing the origin and core formation of the enstatite achondrite parent bodies using Cr isotopes

“…Thermo 2), were also measured in this study to test the data quality. Our data are consistent with previous studies (Bonnand et al, 2016b;Liu et al, 2019;Schoenberg et al, 2016;Sossi et al, 2018;Wu et al, 2020;Zhu et al, 2019c), which suggests that our δ 53 Cr data are accurate to the stated uncertainties.…”

Mass-independent and mass-dependent Cr isotopic composition of the Rumuruti (R) chondrites: Implications for their origin and planet formation

“…The mass-dependent δ 53 Cr data (measured by double spike technique) for BHVO-2 and PCC-1 are also consistent with the literature data (Bonnand et al, 2016b;Liu et al, 2019;Schoenberg et al, 2016;Sossi et al, 2018;Wu et al, 2020;Zhu et al, 2019c).…”

Precise And Accurate Mass-Independent Chromium Isotope Measurement By Total Evaporation Mode On Thermal Ionization Mass Spectrometry (TE-TIMS) At 200 Ng Level

“…(Bio-Rad) resin. AG 50W-X12 resin was used in the chromatography procedure as it as a higher cross-linkage, smaller wet bead size, and smaller molecular weight limits than the Bio-Rad AG50W-X8 (200 ~ 400 mesh), which will give better separation of Cr and Mg. 41 The column chromatography used in this study is described in Table 1 and an example elution curve for the BHVO-2 reference material is shown in Fig. 1.…”

“…The third column contains 0.33 ml of Bio-Rad AG50W-X12 (200 ~ 400 mesh) cation exchange resins. 41 The resin was cleaned with 2 ml 6 M HCl and 1 ml MQ water, then preconditioned with 1 ml 0.5 M HNO3. Samples are loaded in 1 ml 0.5 M HNO3, followed by 2.5 ml (1 + 1.5) 1 M HF to effectively remove residual Ti, Al, Fe and V, and 6 (3 + 3) ml 1 M HCl to remove remaining Mg, K and Ca, and Na.…”