Ohno Takeshi, Hirata Takafumi
Department of Earth and Planetary Sciences, Graduate School of Science and Technology, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro, Tokyo, Japan.
Anal Sci. 2007 Nov;23(11):1275-80. doi: 10.2116/analsci.23.1275.
We present a method to determine (88)Sr/(86)Sr and (87)Sr/(86)Sr simultaneously. The former variation reflects the mass-dependent isotopic fractionation through the physico-chemical processes, and the latter originates from beta(-)-decay of the parent nuclide (87)Rb as well as the mass-dependent isotopic fractionation. In order to determine the mass-dependent isotopic fractionation, the mass-discrimination effect on (88)Sr/(86)Sr was externally corrected by an exponential law using Zr. For the radiogenic growth of (87)Sr/(86)Sr, the mass-dependent isotopic fractionation effect on (87)Sr/(86)Sr was corrected by a conventional correction technique using the (88)Sr/(86)Sr ratio. The reproducibility of the (88)Sr/(86)Sr and (87)Sr/(86)Sr measurements for a high-purity Sr chemical reagent was 0.06 per thousand (2SD, n = 20) and 0.07 per thousand (2SD, n = 20), respectively. Strontium isotopic ratios ((88)Sr/(86)Sr and (87)Sr/(86)Sr) were measured on six geochemical reference materials (igneous rock: JB-1a and JA-2; carbonate mineral: JLs-1, JDo-1, JCp-1 and JCt-1) and one seawater sample. The resulting (87)Sr/(86)Sr ratios obtained here were consistent with previously published data within the analytical uncertainties. The resulting (88)Sr/(86)Sr ratios for igneous rock samples did not vary significantly within the samples, whereas the carbonate samples showed enrichments of the lighter Sr isotopes over the seawater sample. The (88)Sr/(86)Sr ratio of geochemical samples could reflect the physico-chemical processes for the sample formation. Also, a combined discussion of (88)Sr/(86)Sr and (87)Sr/(86)Sr of samples will render multi-dimensional information on geochemical processes.
我们提出了一种同时测定（88）Sr/（86）Sr和（87）Sr/（86）Sr的方法。前者的变化反映了通过物理化学过程的质量依赖同位素分馏，而后者则源于母体核素（87）Rb的β（-）衰变以及质量依赖同位素分馏。为了确定质量依赖同位素分馏，使用Zr通过指数定律对（88）Sr/（86）Sr的质量歧视效应进行了外部校正。对于（87）Sr/（86）Sr的放射性增长，使用（88）Sr/（86）Sr比值通过传统校正技术对（87）Sr/（86）Sr的质量依赖同位素分馏效应进行了校正。对于一种高纯度Sr化学试剂，（88）Sr/（86）Sr和（87）Sr/（86）Sr测量的重现性分别为千分之0.06（2SD，n = 20）和千分之0.07（2SD，n = 20）。在六种地球化学参考物质（火成岩：JB-1a和JA-2；碳酸盐矿物：JLs-1、JDo-1、JCp-1和JCt-1）和一个海水样品上测量了锶同位素比值（（88）Sr/（86）Sr和（87）Sr/（86）Sr）。在此获得的（87）Sr/（86）Sr比值在分析不确定度范围内与先前发表的数据一致。火成岩样品的（88）Sr/（86）Sr比值在样品内部没有显著变化，而碳酸盐样品相对于海水样品显示出较轻Sr同位素的富集。地球化学样品的（88）Sr/（86）Sr比值可以反映样品形成的物理化学过程。此外，对样品的（88）Sr/（86）Sr和（87）Sr/（86）Sr进行综合讨论将提供有关地球化学过程的多维信息。
