Precise Isotope Determination of Trace Amounts of Nd in Magnesium-rich Samples
Precise Isotope Determination of Trace Amounts of Nd in Magnesium-rich Samples
复制标题
DOI：
10.5702/massspec.52.317
复制
发表时间：
2004-12
期刊：
影响因子：
--
通讯作者：
T. Shibata;M. Yoshikawa
中科院分区：
文献类型：
--
作者：
T. Shibata;M. Yoshikawa
我们开发了一种质谱与化学分离相结合的技术，用于分析超镁铁岩样品的Sm-Nd同位素组成，这些样品具有极高的Mg和低Nd浓度，并且一直难以分析。在超镁铁岩中，富Mg在HF分解过程中形成氟化物，少量Sm和Nd强烈地被分配到氟化物中，这将是这些元素回收率低的重要原因，并阻碍了确定可靠的Nd和Sm同位素比值。我们在使用HF和HClO 4的常规方法之前引入了HCl预分解，这使得有可能将回收率提高到85%。另一方面，通过改变Nd+离子流和Nd含量对Nd标准溶液（拉霍亚）进行重复测量，结果表明，在144 Nd+离子流>0.04×10-11 A和Nd含量>2 ng的条件下，可获得可靠的同位素比值。应用该方法分析了美国地质调查局超镁铁岩标准样品PCC-1的143 Nd/144 Nd比值和Sm、Nd含量。我们的分析结果分别为0.512226±0.000026、0.00551±0.00041和0.0278±0.0011 ppm。这些结果是PCC-1的143 Nd/144 Nd比值的首次报道。
We developed a technique combining mass spectrometry with chemical separation to analyze Sm-Nd isotopic compositions of ultramafic rock samples, which have extremely high Mg and low Nd concentrations and are always difficult to analyze. In the case of ultramafic rocks, abundant Mg forms fluorides during decomposition by HF, and minor amounts of Sm and Nd are strongly partitioned into fluorides, which would be a significant reason of low recovery yields of these elements and obstructed to determine a reliable isotopic ratio of Nd and Sm. We introduced pre-decomposition by HCl prior to the conventional method by HF and HClO4 that made it possible to elevate recovery yield to 85%. On the other hand, replicate measurements of Nd standard solution (La Jolla) by changing the ion current of Nd+ and the amount of Nd indicate that reliable isotopic ratios are measured under the condition of >0.04×10-11 A of 144Nd+ ion current and >2 ng of Nd. By applying our method, we analyzed 143Nd/144Nd ratio and Sm and Nd concentrations of PCC-1, which is an ultramafic standard rock sample of United States Geological Survey. The results of our analysis were 0.512226±0.000026, 0.00551±0.00041, and 0.0278±0.0011 ppm, respectively. These results are the first report of 143Nd/144Nd ratio for PCC-1.