Simultaneous measurement of neodymium stable and radiogenic isotopes from a single aliquot using a double spike
Simultaneous measurement of neodymium stable and radiogenic isotopes from a single aliquot using a double spike
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DOI：
10.1039/c9ja00308h
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发表时间：
2020-02
影响因子：
3.4
通讯作者：
A. McCoy-West;M. Millet;G. Nowell;O. Nebel;K. Burton
中科院分区：
文献类型：
--
作者：
A. McCoy-West;M. Millet;G. Nowell;O. Nebel;K. Burton
钕（Nd）稳定同位素有可能对从行星形成和岩浆分异到风化和海洋环流的各种地质过程提供新的约束。在这方面的贡献，我们提出了一种高精度测量Nd稳定同位素比的热电离质谱（TIMS）技术。我们使用由28%145Nd和67%150Nd组成的145 Nd-150 Nd双加标（DS）来校正样品制备和质谱法产生的质量相关分馏。同位素比表示为δ 146 Nd，其是测量的146 Nd/144 Nd比相对于参考材料JNdi-1的每密耳偏差。重复分析表明，δ 146 Nd的内精度（n = 400次; 2se）可达到≤0.005‰，与理论预测一致。一级标准JNdi-1在三年期间的实验室间比较表明，由于法拉第收集器效率的系统偏差，在质谱仪内部和之间引起δ 146 Nd的可分辨偏移。在将数据归一化为JNdi-1 = 0‰后，通过化学分离处理的一系列国际参考物质的δ 146 Nd的长期重现性优于±0.015‰（2 sd）。除了稳定的同位素组成外，该方法还可以同时测量143 Nd/144 Nd，精度≤11 ppm。在143 Nd/144 Nd（0.5118-0.5132）的宽范围内，DS分析在分析不确定度内与使用常规技术的公布值一致。为了对古地质样品（> 2Ga）中的这些放射性同位素组成进行准确的年龄校正，我们首次将DS和元素示踪剂尖峰结合起来。一个149钐示踪剂穗进行校准，并用于获得同位素稀释钐浓度，并最终母-子比。测量的Sm-Nd比在一系列参考物质的先前估计的不确定性范围内，添加Sm尖峰对δ 146 Nd值没有可分辨的影响。该技术允许同时获得δ 146 Nd、143 Nd/144 Nd和Sm/Nd，因此允许对材料的来源或年龄以及其形成过程进行限制。
Neodymium (Nd) stable isotopes have the potential to provide new constraints on a diverse range of geological processes from planetary formation and magmatic differentiation to weathering and ocean circulation. In this contribution, we present a technique for the high-precision measurement of Nd stable isotope ratios by thermal ionisation mass spectrometry (TIMS). We use a 145Nd–150Nd double spike (DS), composed of 28% 145Nd and 67% 150Nd, to correct for mass dependent fractionation resulting from sample preparation and mass spectrometry. Isotope ratios are expressed as δ146Nd which is the per mil deviation in the measured 146Nd/144Nd ratio relative to reference material JNdi-1. Repeated analyses show that an internal precision (n = 400 cycles; 2 se) of ≤0.005‰ on δ146Nd can be achieved in agreement with theoretical predictions. An interlaboratory comparison of the primary standard JNdi-1 over a three-year period shows that resolvable offsets in δ146Nd are induced within and between mass spectrometers as the result of systematic biases in the efficiency of the Faraday collectors. Following normalisation of the data to JNdi-1 = 0‰ the long-term reproducibility of δ146Nd on a range of international reference materials processed through chemical separation is better than ±0.015‰ (2 sd). In addition to stable isotope compositions this method allows for the simultaneous measurement of 143Nd/144Nd with a precision of ≤11 ppm. Over a wide range of 143Nd/144Nd (0.5118–0.5132) the DS analyses here agree within analytical uncertainty with published values using conventional techniques. To allow the accurate age correction of these radiogenic isotope compositions in ancient geological samples (>2 Ga) here for the first time we have combined a DS and an elemental tracer spike. A 149Sm tracer spike was calibrated and used to obtain isotope dilution Sm concentrations and ultimately parent-daughter ratios. Measured Sm–Nd ratios are within uncertainty of previous estimates for a range of reference materials, with the addition of the Sm spike having no resolvable effect on δ146Nd values. This technique allows δ146Nd, 143Nd/144Nd and Sm/Nd to be obtained simultaneously, therefore allowing constrains to be placed on both the source or age of a material and the processes involved in its formation.