锂硼同位素MC-ICP-MS分析中的记忆效应研究

A Study on Memory Effects in Lithium and Boron Isotope Analysis UsingMC-ICP-MS

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δ^(7)Li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δ^(11)B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。

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.Theδ^(7)Li andδ^(11)B 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^(7)Li background signal is less than 5mV within 24h.The long-term external precision ofδ^(7)Li values for Alfa Li,an in-house standard,was 0.13‰(2SD,n=73).Rinsing solutions,such as NAF and NH_(3)·H_(2)O could not significantly reduce the boron background of the instrument.However,the flexible blank subtracting method was used for precise determination ofδ^(11)B values.The long-term external precision ofδ^(11)B values for Alfa B was 0.19‰(2SD,n=60).The averageδ^(7)Li andδ^(11)B 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.