A low-blank two-column chromatography separation strategy based on a KMnO4 oxidizing reagent for Cr isotope determination in micro-silicate samples by thermal ionization mass spectrometry
A low-blank two-column chromatography separation strategy based on a KMnO4 oxidizing reagent for Cr isotope determination in micro-silicate samples by thermal ionization mass spectrometry
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DOI：
10.1039/c7ja00225d
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发表时间：
2017-10
影响因子：
3.4
通讯作者：
Chaofeng Li;Lianjun Feng;Xuan‐Ce Wang;S. Wilde;Zhuyin Chu;Jing-hui Guo
中科院分区：
文献类型：
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作者：
Chaofeng Li;Lianjun Feng;Xuan‐Ce Wang;S. Wilde;Zhuyin Chu;Jing-hui Guo
本研究建立了一种从小硅酸盐样品（0.3-2 mg）中分离Cr的新技术，并利用双峰热电离质谱法（DS-TIMS）测定硅酸盐中Cr的稳定同位素。基于我们最近的两步交换树脂方案（Li et al.， JAAS, 2016, 31, 2375），我们进一步显著减少了程序空白，提高了从安山岩到超基性岩以及碳酸盐组成的一系列复杂硅酸盐岩石的Cr回收率（94.7% - 97.5%）。改进的关键是用KMnO4代替了传统的（NH4）2S2O8作为氧化剂，将之前研究中的程序空白从1-20 ng减少到0.15±0.04 ng （n = 8）。此外，在TIMS测量中，传统方法中残余SO42−对Cr信号的抑制作用已经完全消除。这允许从小至~ 46 ng的地质样品中高精度地测定Cr同位素比率。用0.3-2 mg大小范围内的各种硅酸盐岩石验证了该化学过程。一系列分析表明，它可以达到±0.03至0.06‰的内部精度（2 SE）。对0.3 mg （δ53Cr = - 0.158±0.052‰，2 SD）的玄武岩标准BIR-1样品进行重复消化和分析表明，对于极小的硅酸盐样品，该方法具有良好的中间精度。
This study has led to a new technique for the separation of Cr from small silicate samples (0.3–2 mg) and determination of stable Cr isotopes in silicates by double spike thermal ionization mass spectrometry (DS-TIMS). Based on our recent two-step exchange resin scheme (Li et al., JAAS, 2016, 31, 2375), we further significantly reduced the procedural blank and improved Cr recovery (94.7–97.5%) from a range of complex silicate rocks varying in composition from andesite to ultra-mafic, and carbonates as well. The key improvement is that KMnO4 was employed to replace conventional (NH4)2S2O8 as the oxidizing reagent, which reduces the procedural blank from 1–20 ng in previous studies to 0.15 ± 0.04 ng (n = 8). In addition, the inhibition effect on the Cr signal caused by residual SO42− in the Cr fraction using the conventional method has been completely eliminated during TIMS measurements. This permits the high precision determination of Cr isotopic ratios from geological samples as small as ∼46 ng. This chemical procedure was verified using a variety of silicate rocks in the size range of 0.3–2 mg. A series of analyses demonstrated that it is possible to attain internal precisions (2 SE) of ±0.03 to 0.06‰. Replicate digestions and analyses of basalt standard BIR-1 with a sample size of 0.3 mg (δ53Cr = −0.158 ± 0.052‰, 2 SD) demonstrated that good intermediate precision is obtainable for extremely small silicate samples.