Precise determination of Sm, Nd concentrations and Nd isotopic compositions at the nanogram level in geological samples by thermal ionization mass spectrometry
Precise determination of Sm, Nd concentrations and Nd isotopic compositions at the nanogram level in geological samples by thermal ionization mass spectrometry
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采用热电离质谱法精确测定地质样品中纳克级的 Sm、Nd 浓度和 Nd 同位素组成
DOI：
10.1039/b904047a
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发表时间：
2009-01-01
影响因子：
3.4
通讯作者：
Guo, Jinhui
中科院分区：
文献类型：
--
作者：
Chu, Zhuyin;Chen, Fukun;Guo, Jinhui
本文提出了一种用TaF_5作离子发射体的单钨丝TIMS测量Nd同位素（NdO ~+）的高灵敏度方法。虽然分析Nd同位素的氧化物（NdO+）是一个众所周知的技术，这是第一次报告，分析Nd同位素组成的氧化物使用W灯丝和TaF 5发射体。当使用该方法测量0.5-1 ng负载的NeoCl同位素参考试剂JNdi-1时，发现离子产率大多超过15%，并且可以高达32%。对于1 ng JNdi-1上样量，143 Nd/144 Nd的内部精密度可优于10 ppm（2SE），对于0.5 ng JNdi-1上样量，143 Nd/144 Nd的内部精密度可优于15 ppm（2SE）; 0.5-1 ng JNdi-1上样量的13份重复样品产生的143 Nd/144 Nd值为0.512112 ± 0.000028（2SD）。与以往报道的采用Re（或W）灯丝+硅胶+H_3PO_4负载技术的NdO ~+测量方法相比，该方法具有灵敏度高、离子束稳定性好、无需向离子源室中流血的氧气等优点。使用W灯丝和TaF 5发射器分析Sm同位素为Sm+，并且还获得了高灵敏度和良好的离子束稳定性。采用全柱化学和TaF_5法分析了几种国际岩石标准物质，其中包括一种超镁铁岩标准物质USGS PCC-1，该标准物质中Sm和Nd含量极低，其Sm、Nd含量和Nd同位素数据与文献报道值吻合较好。结合高效和低空白柱化学分离Nd的Sm，Ce和Pr，这种方法具有潜在的分析Sm，Nd浓度和Nd同位素组成的高度亏损的橄榄岩;非常小的等分试样的矿物，如石榴石;有限的样品大小的地球外材料;和环境样品，含有非常低的Sm和Nd的量。
In this paper, a high sensitivity method for measurements of Nd isotopes as NdO+, on a TIMS using a single W filament with TaF5 as an ion emitter is presented. Although analyzing Nd isotopes as oxides (NdO+) is a well known technique, this is the first report to analyze Nd isotopic compositions as oxides using W filaments and the TaF5 emitter. When 0.5–1 ng loads of a Neodymium isotopic reference reagent, JNdi-1, were measured using this method, the ion yields were found to be mostly in excess of 15% and could be as high as 32%. Internal precision on 143Nd/144Nd could be better than 10 ppm (2SE) for 1 ng JNdi-1 loads and better than 15 ppm (2SE) for 0.5 ng JNdi-1 loads; thirteen replicates of 0.5–1 ng JNdi-1 loads yielded a 143Nd/144Nd value of 0.512112 ± 0.000028 (2SD). Compared with the previously reported NdO+ measurement method using the Re (or W) filaments + Silica-gel + H3PO4 loading techniques, this method has advantages including higher sensitivity, a more stable ion beam, and no need for oxygen gas to be bled into the ion source chamber. Sm isotopes were analyzed as Sm+ using the W filaments and the TaF5 emitter, and high sensitivity and good ion beam stability were also obtained. Several international rock reference materials, including an ultramafic rock reference material USGS PCC-1 that contains very low amounts of Sm and Nd, were analyzed with full column chemistry and the TaF5 method, and the results of Sm, Nd concentrations and Nd isotopic data are in good agreement with the reported values. Combined with a highly efficient and low-blank column chemistry to separate Nd from Sm, Ce, and Pr, this method holds potential to analyze Sm, Nd concentrations and Nd isotopic compositions of highly depleted peridotites; very small aliquots of minerals such as garnets; extra-terrestrial materials of limited sample size; and environmental samples that contain very low quantities of Sm and Nd.