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摘要:
锂(Li)和硼(B)同位素是地质作用过程中良好的示踪剂，被广泛应用于岩石起源、矿床成因和环境演化等领域。但锂、硼在MC-ICP-MS仪器分析中的“记忆效应”明显，不同实验室已报道的MC-ICP-MS分析中锂、硼背景占信号比变化范围大(0.01%～5%)，所采用的背景控制方法和效果也各不相同，因此给锂、硼同位素的准确测定带来困难。为研究MC-ICP-MS锂、硼同位素记忆效应及其抑制方案，提高测试的稳定性，本文参考前人研究成果，设计不同背景清洗方案，并对各种国际标样(IRMM-016、JG-2、ERM-AE121、ERM-AE122、NASS-7)和实验室内部标准(Alfa Li、Alfa B)进行长期测试，检验实验方案的长期重现性。结果表明：仅使用0.3%氯化钠溶液清洗背景可以显著降低锂背景信号，从20mV下降至4mV，并保证7Li背景值在24h内低于5mV，实验室内部标准溶液Alfa Li的δ7Li长期测试外精度为0.13‰(2SD，n=73)。氟化钠、氨水等清洗液并不能显著降低本研究所使用仪器的硼背景，因此选择使用灵活的空白扣除方法来保证数据稳定性。实验室内部标准溶液Alfa B的δ11B长期测试外精度为0.19‰(2SD，n=60)。本文锂、硼同位素国际标样的测试结果与前人数据在误差范围内一致，证明了实验结论的可靠性。
Abstract:Lithium (Li) and boron (B) isotopes are excellent tracers in geological processes. In order to study and eliminate the memory effects of lithium and boron element in isotopic measurements using MC-ICP-MS, different background rinsing protocols were designed with reference to previous research. The δ7Li and δ11B values of different types of reference materials were tested to evaluate the long-term reproducibility of the measurements using designated rinsing protocols for at least six months. The results show that using only 0.3% NaCl solution to clean the background for 60s can significantly reduce the lithium background signal and ensure the 7Li background signal is less than 5mV within 24h. The long-term external precision of δ7Li values for Alfa Li, an in-house standard, was 0.13‰ (2SD, n=73). Rinsing solutions, such as NAF and NH3·H2O could not significantly reduce the boron background of the instrument. However, the flexible blank subtracting method was used for precise determination of δ11B values. The long-term external precision of δ11B values for Alfa B was 0.19‰ (2SD, n=60). The average δ7Li and δ11B values of different types of reference materials were tested using these rinsing protocols, and the results were well consistent with reported data, supporting the applicability of the conclusions. The BRIEF REPORT is available for this paper at
http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202310260167 .-
Key words:
- memory effect /
- lithium /
- boron /
- MC-ICP-MS /
- 0.3% NaCl solution /
- blank deduction
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图 2 5%氯化钠溶液清洗背景60s后，在正常测试过程中样品7Li灵敏度(200ng/g)、7Li背景(a)和7Li/6Li 测试内精度(SE)(b)的变化
Figure 2.
图 7 标准样品EPM-AE 121(a)、EPM-AE 122(b)、Alfa B(c)和NASS-7(d)相对于NIST951a的δ11B测定值及其参考值
Figure 7.
表 1 Nu Sapphire MC-ICP-MS仪器基本配置
Table 1. Basic configuration of the Nu Sapphire MC-ICP-MS instrument
工作参数 实验条件 工作参数 实验条件 射频功率 1300W 炬管 石英炬管 加速电压 6000V，高能模式 雾化器气体(Ar)压力 ～30psi 冷却气(Ar)流速 13L/min 锥 镍锥，湿锥 辅助气(Ar)流速 0.9～1.0L/min 接收器设置 H6-11B；L6-10B
H9-6Li；L6-7Li雾化器及流速 玻璃雾化器，PFA雾化器，100/50μL/min 分辨率 低分辨 
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表 2 标准物质锂同位素组成测定值与参考值
Table 2. The measured and reported δ7LiL-SVEC values of standards
标准物质 δ7LiL-SVEC参考值
(‰)δ7LiL-SVEC测试值
(‰)2SD
(‰)n IRMM-016 −0.17～0.40a 0.12 0.07 50 USTC-Li −19.30b −19.37 0.12 56 Alfa Li − 13.71 0.13 73 JG-2 0.15～0.32c 0.13 0.11 12 注：“−”表示无参考值。Alfa Li为实验室内部标准溶液，无参考值。a. IRMM-016的δ7LiL-SVEC参考值来源于GeoReM(Geological and Environmental Reference Materials)数据库及对应参考文献，仅统计MC-ICP-MS测试结果。b. USTC-Li 的δ7LiL-SVEC参考值由中国科技大学肖益林教授提供。c. JG-2的δ7LiL-SVEC参考值来源于Bouman等(2004)［30］、Jeffcoate等(2004)［15］、Li 等(2019)［31］、Lin等(2016)［32］和Zhu等(2020)［33］。
Note:“−” indicates the absence of a reference value. Alfa Li serves as the internal standard solution in the laboratory，and no reference value is available. a. The δ7LiL-SVEC reference value of IRMM-016 is derived from the Geological and Environmental Reference Materials (GeoReM) database and corresponding references，considering only the MC-ICP-MS test results. b. The δ7LiL-SVEC reference value of USTC-Li is provided by Professor Xiao Yilin from the University of Science and Technology of China. c. The δ7LiL-SVEC reference values of JG-2 are derived from Bouman et al. (2004) [30］，Jeffcoate et al. (2004) ［15］，Li et al. (2019) ［31］，Lin et al. (2016) ［32］ and Zhu et al. (2020) ［33］.
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表 3 标准物质硼同位素组成测定值与参考值
Table 3. The determined values and reference values of the B isotope composition in the reference materials
标准物质 δ11BNIST951参考值
(‰)δ11BNIST951a测试值
(‰)2SD
(‰)n ERM-AE121 19.54～20.33a 19.78 0.31 64 ERM-AE122 39.3～39.74a 39.54 0.33 36 Alfa B − −4.66 0.19 60 海水标样NASS-7 − 40.03 0.33 35 天然海水 39.98±0.35b − − − 天然海水 39.45～40.26b − − − 海水标样NASS-2 39.63～39.90c − − − 海水标样NASS-5 39.40～39.89c − − − 海水标样NASS-6 39.41～39.81c − − − 注：“−”表示无参考值。Alfa B为实验室内部标准溶液，无参考值。a. ERM-AE121和ERM-AE122的δ11BNIST 951参考值来自GeoReM数据库及对应参考文献。数据包括了样品相对于NIST SRM951和NIST SRM951a的参考值。b. 天然海水δ11BNIST 951参考值引自Chen等(2019)［27］及其中参考文献。c. NASS系列海水δ11BNIST 951参考值引自GeoReM数据库及对应参考文献。
Note: “−” indicates the absence of a reference value. Alfa B is a laboratory standard solution without a designated reference value. a. The δ11BNIST 951 reference values of ERM-AE121 and ERM-AE122 are from the GeoReM database and corresponding references. The data include reference values of the sample with respect to NIST SRM951 and NIST SRM951a. b. The reference value of δ11BNIST 951 in natural seawater is cited from Chen et al. (2019) ［27］ and other references. c. The reference value of δ11BNIST 951 for NASS series seawater is sourced from the GeoReM database and corresponding references.
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