Determination of Mass-Dependent Isotopic Fractionation of Cerium and Neodymium in Geochemical Samples by MC-ICPMS
Determination of Mass-Dependent Isotopic Fractionation of Cerium and Neodymium in Geochemical Samples by MC-ICPMS
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DOI：
10.2116/analsci.29.47
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发表时间：
2013-01-01
影响因子：
1.6
通讯作者：
Hirata, Takafumi
中科院分区：
文献类型：
--
作者：
Ohno, Takeshi;Hirata, Takafumi
我们开发了一种新的分析方法来测定地球化学样品中Ce和Nd的质量依赖同位素分馏。通过正态化Sm-149/Sm-147和Eu-153/Eu-151，根据指数规律对Ce和Nd的质量歧视效应进行了外部校正，分别为0.92124和1.0916。Ce-142/Ce-140、Nd-146/Nd-144和Nd-148/Nd-144同位素比测量的重现性分别为0.08‰（2SD, n = 25）、0.06‰（2SD, n = 39）和0.12‰（2SD, n = 39）。应用本方法测定了5种地球化学参考物质（火成岩、JB-1a和JA-2；沉积岩、JMn-1、JCh-1和JDo-1）的Ce和Nd同位素比值的变化。两种火成岩（JB-1 a和JA-2）和两种沉积岩（JMn-1和JCh-1）的同位素比值在样品之间没有显著差异，而碳酸盐样品（JDo-1）的Ce和Nd同位素比值显著高于火成岩和沉积岩样品。Ce-142和Nd-146呈1:1的简单相关关系，表明Ce和Nd的同位素分馏程度没有显著差异。这表明JDo-1中Ce的同位素分馏可能是由地球化学或物理化学过程引起的，而不改变Ce的氧化状态，因为氧化还原反应比不改变氧化状态的反应产生更大的同位素分馏。地球化学样品中Ce和Nd同位素比值的变化可以为样品形成的物理化学过程提供新的信息。
We have developed a new analytical method to determine the mass-dependent isotopic fractionations on Ce and Nd in geochemical samples. Mass discrimination effects on Ce and Nd were externally corrected by normalizing Sm-149/Sm-147 and Eu-153/Eu-151, being 0.92124 and 1.0916, respectively based on an exponential law. The reproducibility of the isotopic ratio measurements on Ce-142/Ce-140, Nd-146/Nd-144 and Nd-148/Nd-144 were 0.08 parts per thousand (2SD, n = 25), 0.06 parts per thousand (2SD, n = 39) and 0.12 parts per thousand (2SD, n = 39), respectively. The present technique was applied to determine the variations of the Ce and Nd isotopic ratios for five geochemical reference materials (igneous rocks, JB-1a and JA-2; sedimentary rocks, JMn-1, JCh-1 and JDo-1). The resulting ratios for two igneous rocks (JB-1 a and JA-2) and two sedimentary rocks (JMn-1 and JCh-1) did not vary significantly among the samples, whereas the Ce and Nd isotope ratios for the carbonate samples (JDo-1) were significantly higher than those for igneous and sedimentary rock samples. The 1:1 simple correlation between delta Ce-142 and delta Nd-146 indicates that there were no significant difference in the degree of isotopic fractionation between the Ce and Nd. This suggests that the isotopic fractionation for Ce found in the JDo-1 could be induced by geochemical or physicochemical processes without changing the oxidation status of Ce, since the redox-reaction can produce larger isotopic fractionation than the reactions without changing the oxidation state. The variations in the Ce and Nd isotope ratios for geochemical samples could provide new information concerning the physico-chemical processes of the sample formation.