In situ Nd isotopic analysis of geological materials by laser ablation MC-ICP-MS
In situ Nd isotopic analysis of geological materials by laser ablation MC-ICP-MS
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DOI：
10.1039/b513945g
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发表时间：
2006-01-01
影响因子：
3.4
通讯作者：
Vance, D
中科院分区：
文献类型：
--
作者：
Foster, GL;Vance, D
钕(ND)同位素在地球科学中有着广泛的应用，无论是在年代学方面，还是在物源/示踪研究方面。传统上，同位素分析是通过从样品基质中化学分离纯Nd来完成的。这一过程非常耗时，并且可能会丢失在小空间尺度上保存的大量信息。在这里，我们描述了一种激光消融方案，用于测量具有相对较高浓度(~gt；=100ppm；例如，磷灰石、钛铁矿和铁锰结核)的地质材料中的Nd同位素。该程序首次允许在小于0.1毫米的尺度上利用存储在ND同位素中的信息。需要克服的主要分析问题是等压Sm同位素的干扰，对干扰的校正必须非常准确，以便保持对ND同位素比值的高精度。我们指出，仔细注意质量鉴别效应以及迭代校正过程可以使Sm/ND比值高达1.2时的Nd143/Nd144同位素比值的精度达到0.5epsilon单位的数量级(0.005%)。总分析时间很短(类似于2-5分钟)，可在每个分析会话中进行大量分析(>；30)。空间分辨率受Nd浓度和所需精度的制约，对于磷灰石和钛矿，空间分辨率通常类似于90微米。相对于最好的TIMS和溶液MC-ICPMS数据，分析精度下降了约2-3倍。然而，至关重要的是，到目前为止，快速的样本吞吐量和极高的空间分辨率远远超过了精度的下降。对大西洋铁锰结壳的高分辨率研究表明了所述方法的实用性。
Neodymium (Nd) isotopes have widespread applications in the earth sciences, both in geochronology and in provenance/tracer studies. The isotopic analyses are conventionally done by chemical separation of pure Nd from the sample matrix. This process is time consuming and loses potentially vast amounts of information held at small spatial scales. Here, we describe a laser ablation protocol for the measurement of Nd isotopes in geological materials with relatively high Nd concentrations (>= 100 ppm; e.g., apatite, titanite, and ferromanganese nodules). The procedure allows, for the first time, the exploitation of information held in Nd isotopes at scales of less than 0.1 mm. The principal analytical issues to be overcome are the interferences from isobaric Sm isotopes, the correction for which must be very accurate in order to maintain a high accuracy for the Nd isotopic ratios. We show that careful attention to mass discrimination effects along with an iterative correction procedure allows a correction that results in an accuracy on the Nd-143/Nd-144 isotope ratio of the order of 0.5 epsilon units (0.005%) for Sm/Nd ratios as high as 1.2. The total analysis time is short (similar to 2 - 5 min), enabling a large number of analyses (> 30) in each analytical session. Spatial resolution is governed by the Nd concentration and the required accuracy and for apatites and titanites it is typically similar to 90 mu m. Analytical precision is degraded by around a factor of 2 - 3 relative to the best TIMS and solution MC-ICP-MS data. Crucially, however, the rapid sample throughput and the extremely high spatial resolution by far outweigh this reduction in precision. A high resolution study of an Atlantic ferromanganese crust illustrates the usefulness of the described approach.