Accurate measurement of chromium isotopic compositions in geological reference materials by double-spike mc‐icp‐ms

Abstract

The δ53/52Cr values of twenty-five geological reference materials (GRMs) were determined including igneous rocks, coal, shale, stream/ocean sediments and soils, with high-precision double spike MC-ICP-MS (Neptune Plus). Previously measured GRMs, including MUH-1, OKUM, DTS-2B, and JB-3, were used to monitor the long-term analytical precision and accuracy. The resulting method yielded a long-term precision of ≤ 0.06‰ based on these GRMs, and the δ53/52Cr values were excellently consistent with their previously reported values. Most of the seventeen new GRMs reported here yielded δ53/52Cr values within a narrow range from-0.20‰ to 0.01‰, with an average of-0.14 ± 0.10‰(2SD), which was the same as the unfractionated Bulk Silicate Earth (BSE). However, SCO-2 (shale) yielded a δ53/52Cr value of 0.19 ± 0.03‰ (2SD) and GBW07334 (ocean sediment) yielded a δ53/52Cr value of 0.01 ± 0.05‰ (2SD), which were different from the BSE. Thus, SCO-2 and JH-1 (-0.20 ± 0.02‰) can serve as good candidate GRMs for interlaboratory comparisons.