Lithium isotopic analysis of rocks: using multiple-collector ICP-MS
Date Issued
2014
Date
2014
Author(s)
Yang, Bin-Hao
Abstract
Lithium (Li) has two stable isotopes, Li6and Li7, with large mass difference. Their isotopic fractionation significantly occurs in the interaction between soild/rock and aqueous phase/water in low termperature, and thus lithium isotopes have high potential as a geochemical tracer for aqueous-related geological processes, e.g. weathering on the Earth’s surface and dehydration of altered oceanic crust in subduction zones. The goal of this study is to establish the method of Li isotopes in igneous rocks in NTU as a base of future researches. At beginning, approximately 25 mg powder of international reference rocks, from peridotite to rhyolite or granite, were digested by inorganic acids completely. Chemical separation was followed and sample solution was eluted through 1.6 ml AG50W-X8 cation exchange resin by 1 M HNO3-80% (v/v) methanol to set up elution curves. According to the elution curves, the Li fraction of each sample with >99% recovery yield was collected and then quantitatively analysed by ICP-QMS and MC-ICP-MS for its matrix elements and lithium isotopes, δ7Li, respectively. In MC-ICP-MS analysis, zero was determined at each mass peak center of a blank solution, and the “standard-sample-standard bracketing” method was adopted in order to correct for the mass bias. Our preliminary results indicate: The elution curve of Li slightly varies with lithology. Li fraction of ultramafic and mafic rock samples may have matrices that concentrations are higher than Li, i.e. sodium and titanium, respectively. However, such high-abundance impurities do not affect our lithium isotopic measurements demonstrated by analysing doped with L-SVEC. Long-term precision of this study is 0.5‰ (2 S.D.). δ7Li values measured of USGS RMs (BHVO-2: +4.5‰ AGV-2: +7.3‰ G-2: -0.4‰ RGM-1: +2.8‰) are consistent with literature values.
Subjects
鋰同位素
多接收感應耦合電漿質譜儀
提洗曲線
標準品—樣品—標準品包圍法
Type
thesis
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