Precise measurement of Cr isotope ratios using a highly sensitive Nb2O5 emitter by thermal ionization mass spectrometry and an improved procedure for separating Cr from geological materials
Precise measurement of Cr isotope ratios using a highly sensitive Nb2O5 emitter by thermal ionization mass spectrometry and an improved procedure for separating Cr from geological materials
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使用高灵敏度 Nb2O5 发射器通过热电离质谱法精确测量 Cr 同位素比，并改进从地质材料中分离 Cr 的程序
DOI：
10.1039/c6ja00265j
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发表时间：
2016-11
影响因子：
3.4
通讯作者：
Wilde SA
中科院分区：
文献类型：
--
作者：
Wang XC;Chu ZY;Guo JH;Wilde SA
铬同位素在宇宙化学、环境科学、地球化学和古海洋学研究中具有重要应用。在之前的研究中，热电离质谱 (TIMS) 在 Cr 同位素比率分析方面表现出出色的精度。然而，TIMS 测量需要相对较大的样本量（200-2000 ng），因此阻碍了其在地球科学和环境科学中的更广泛应用。在这项研究中，首次采用高灵敏度的 Nb2O5 发射器通过 TIMS 测量 Cr 同位素。这种Nb2O5发射器的灵敏度至少提高了10倍，不仅可以显着减小样品尺寸，而且可以获得良好的外部精度。在本研究中，5 ng NIST SRM 3112a 标准样品的 δ53Cr 外部精度为 ±0.23‰（2 SD，n = 10）。此外，还设计了一种改进的两柱化学分离程序，以便从复杂的地质材料中分离铬。与经典的阴离子树脂纯化方法相比，通过仔细优化和评估(NH4)2S2O8氧化剂的用量，显着降低了程序空白和SO42−的严重抑制作用。该方法已使用一种白云石、三种玄武岩和一种橄榄岩参考材料进行了验证。一系列分析测试表明，单次 30 分钟分析可以获得 ±0.017 至 0.037‰ 的内部精度 (2 SE)。 53Cr/52Cr 的长期再现性 (2 SD) 为 0.113454 ± 0.000004 (∼0.035‰)，通过 NIST SRM 3112a 在 6 个月内的重复分析 (n = 105) 获得。玄武岩标准品 BIR-1 (δ53Cr = −0.110 ± 0.048‰, 2 SD) 和碳酸盐标准品 JDo-1 (δ53Cr = 1.710 ± 0.054‰, 2 SD) 的重复消解和分析表明，天然样品可以获得良好的外部重现性。
Chromium isotopes have important applications in cosmochemistry, environmental science, geochemistry, and paleoceanography studies. In previous investigations, thermal ionization mass spectrometry (TIMS) showed excellent precision for Cr isotopic ratios analysis. However, relative large sample sizes (200–2000 ng) were required for TIMS measurements and therefore hampered its wider application in geoscience and environmental science. In this study, a highly sensitive Nb2O5 emitter is employed for the first time to measure Cr isotopes using TIMS. This Nb2O5 emitter produces at least a 10-fold enhancement in the sensitivity and can not only significantly reduce the sample size, but also obtain good external precision. In this study, an external precision of ±0.23‰ (2 SD, n = 10) on δ53Cr was obtained on a 5 ng sample of NIST SRM 3112a standard. In addition, an improved two-column chemical separation procedure was devised in order to separate Cr from complex geological materials. Compared to the classical anion resin purification method, the procedural blank and severe inhibition effect from SO42− is significantly reduced by carefully optimizing and evaluating the dosage of (NH4)2S2O8 oxidant. This method has been verified using one dolomite, three basalt and one peridotite reference materials. A range of analytical tests demonstrates that it is possible to attain internal precisions (2 SE) of ±0.017 to 0.037‰ on a single 30 min analysis. Long-term reproducibility (2 SD) for 53Cr/52Cr is 0.113454 ± 0.000004 (∼0.035‰) obtained by replicate analyses (n = 105) of NIST SRM 3112a over a 6 month period. Replicate digestions and analyses of the basalt standard BIR-1 (δ53Cr = −0.110 ± 0.048‰, 2 SD) and the carbonate standard JDo-1 (δ53Cr = 1.710 ± 0.054‰, 2 SD) demonstrate that good external reproducibility is obtainable on natural samples.
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