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《Geochimica》 2017-06
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Efficient purification for Li and high-precision and accuracy determination of Li isotopic compositions by MC-ICP-MS

GOU Long-fei;JIN Zhang-dong;DENG Li;SUN He;YU Hui-min;ZHANG Fei;State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences;University of Chinese Academy of Sciences;Institute of Global Environmental Change, Xi'an Jiaotong University;Key Laboratory of Crust-Mantle Materials and Environments of Chinese Academy of Sciences, School of Earth and Space Sciences, University of Science and Technology of China;  
Efficient isolation and purification of lithium(Li) were accomplished for various environmental and geological samples by a series of iterative experiments. These experiments led to the creation of a set of recommended experimental conditions including an 8 m L column volume, AG 50 W-X12 resin, and 0.5 mol/L HNO3 eluent. Eluate was collected during a single leach in the volume interval between 20 and 48 m L to achieve a complete purification and recovery of Li. Nevertheless, for samples in a hyperhaline matrix, a double purification procedure is suggested to ensure that Na/Li 1, which is essential for measuring the isotopic composition of Li on a multi-collector inductively coupled plasma mass spectrometer(MC-ICP-MS). In this work, isotopic composition was determined using a Neptune Plus MC-ICP-MS. The δ7 Li of a laboratory-mixed solution(IEECAS-Li) purified by our procedure was measured to be 8.31‰ ± 0.12‰, which is in agreement with that of the corresponding single element standard before mixing, 8.33‰ ± 0.20‰. Following our purification procedure, the δ7 Li values of USGS international rock reference materials(AGV-2 and BHVO-2) and seawater reference material NASS-6 were measured as 6.83‰ ± 0.75‰, 4.32‰ ± 0.33‰, and 31.10‰ ± 0.60‰(2 s.d., n = 5), respectively, all of which are within the range of error of the reported values. As a result, we propose a one-step purification procedure for Li and then an accurate and high-precision determination of its isotopic compositions by MC-ICP-MS. The purification protocol was then used to separate Li from samples of river water, lake water, and loess. The multiply measured δ7 Li values of six such samples with Li concentrations ranging from 15 ng/g to 90 μg/g had two-time standard derivations better than 0.30‰ with excellent reproducibility, demonstrating the high-level precision and the accuracy possible for Li isotopic measurements. This purification protocol is especially suitable for environmental samples with very low Li contents.
【Fund】: 国家自然科学基金(41225015);; 国家重点研发计划“全球变化及应对”专项(2013CB956402)
【CateGory Index】: P597
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