High precision determination of chromium isotope ratios in geological samples by MC-ICP-MS
High precision determination of chromium isotope ratios in geological samples by MC-ICP-MS
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DOI：
10.1039/b808351g
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发表时间：
2008-11
影响因子：
3.4
通讯作者：
L. Halicz;Lu Yang;N. Teplyakov;A. Burg;R. Sturgeon;Y. Kolodny
中科院分区：
文献类型：
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作者：
L. Halicz;Lu Yang;N. Teplyakov;A. Burg;R. Sturgeon;Y. Kolodny
本工作描述了多接收电感耦合等离子体质谱（MC-ICP-MS）的铬同位素比值（50 Cr/52 Cr，53 Cr/52 Cr和54 Cr/52 Cr）的精确和准确的测定方法。使用“标准品-样品-标准品”交叉进样技术和NIST SRM 979 Cr（NO3）3·9 H2O标准化校正质量鉴别和仪器漂移。50 Cr/52 Cr、53 Cr/52 Cr和54 Cr/52 Cr比值的测量精度（2s）分别为±0.11‰、±0.06‰和±0.10‰（110 ppm、60 ppm和100 ppm）。对于浓度较高（300 ~ 17000 ppm）的地质样品，用阴、阳离子交换树脂柱将铬从基体中分离出来，回收率> 95%。令人费解的是，对于一些地质样品，上述方法不能有效地将Fe和Ti的浓度降低到低于2%，相对于铬的浓度。因此，在这些样品中仅测定了53 Cr/52 Cr。在标准（NIST SRM 979）、化学纯的Cr金属碎片（Alfa Aesar）、晚元古代辉长岩、白垩纪油页岩和油页岩燃烧变质的天然产物之间发现同位素比的显著差异。火成岩和纯金属的δ53/52 Cr值略负，油页岩为+1.01‰，燃烧变质产物的δ 53/52 Cr值均较轻，表明较重的铬同位素在变质过程中被去除。
The present work describes methodology for the precise and accurate determination of chromium isotope ratios (50Cr/52Cr, 53Cr/52Cr, and 54Cr/52Cr) by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Mass discrimination and instrument drift are corrected for using a “standard–sample–standard” bracketing technique and normalization against NIST SRM 979 Cr(NO3)3·9H2O. The precisions (2s) of ratio measurements for 50Cr/52Cr, 53Cr/52Cr, and 54Cr/52Cr are ±0.11‰, ±0.06‰, and ±0.10‰ (110 ppm, 60 ppm and 100 ppm), respectively. For geological samples of relatively high concentration (300–17 000 ppm), Cr was separated from the matrix using columns of anion and cation exchange resins, providing a recovery of >95%. Inexplicably, for some geological samples, the aforementioned methodologies were not effective in reducing the concentrations of Fe and Ti to below 2% relative to the Cr concentration in the eluate. As a consequence, only 53Cr/52Cr was determined in such samples. Significant differences in isotope ratios were found among standard (NIST SRM 979), chemically pure metal chips of Cr (Alfa Aesar), a Late Proterozoic gabbro, a Cretaceous oil shale and natural products of combustion metamorphism of that oil shale. The igneous rocks and the pure metal have slightly negative δ53/52Cr values, the oil shale is +1.01‰, and the products of combustion metamorphism are all somewhat lighter, suggesting that the heavier isotopes of chromium were removed in the process of metamorphism.