| The relative large lithium isotopic fractionation in natural samples has useful application in the fields of geochemistry, cosmo-chemistry and nuclear chemistry. All these fields require precise measurement of the ~7Li/~6 Li ratio. There are visible interferers in the process of measurement due to trace element, so we must prepare the natural samples before determination of lithium isotopic composition, including separation, enrichment and purification. In this thesis, the solution of Chinese reference materials including lithium, potassium, calcium, sodium, magnesium, was used to evaluate analytical methods applied. Lithium was enriched in different eluents (hydrochloric acid, nitric acid and mixture with ethanol or methanol) by cation exchange resin AG 50W-X8, and the optional experimental conditions were studied. Some main conclusions are listed as follows:1 , Setting up a rapid and valid method which separate lithium from other elements by one column. This method only uses 0.15M HC1 as eluent, and operation is very simple.2, The influence of potential sources of error for acquisition of lithium isotopic data introduced during the separation, such as matrix effects and isotopic fractionation due to incomplete recovery, were examined by using artificial mixed solution. The examinations demonstrated that our protocol suffered from negligible isotopic fractionation.3, MC-ICP-MS was applied to lithium isotopic measurements. Based on multiple duplicate and replicate measurements, the precision of this method is conservatively estimated to be 0.8‰ (2σ), which is similar to the precision of other method by TIMS. The δ~7Li value determined for sea water is +31.8‰, which agree well with those of previously reported datum.4, This method can be applied to some samples having low concentration of lithium. We determined lithium isotope of some seawater, rock and soil samples in which concentration of lithium rang from 0.064μg/g to 132μg/g, so the method is fit for low lithium reservoirs.
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