MC-ICP-MS高精度测定Li同位素分析方法

High-precision measurement of lithium isotopes using MC-ICP-MS.

以不同浓度Li元素标准样品和K、Ca、Na、Mg、Fe单元素标准样品的混合溶液为研究对象,采用3根阳离子交换树脂（AG50 W-X8,200-400目）填充的聚丙烯交换柱和石英交换柱对Li进行分离富集,淋洗液分别为2.8 mol/L HCl、0.15 mol/L HCl以及0.5 mol/L HCl 30%乙醇,淋洗液体积小,仅为38 mL。分离回收率高,均大于97.6%。国际标样AGV-2（相对于IRMM-016）、BHVO-2（相对于IRMM-016）和IRMM-016（相对于L-SVEC）的δ7Li值分别为（5.13±0.94）‰（2σ,n=10）、（4.08±0.60）‰（2σ,n=4）和（0.038±0.73）‰（2σ,n=10）,与前人分析结果吻合,分析精度与国际同类实验室水平相当。并对比了马里兰大学同位素实验室和笔者实验室对同种岩石矿物样品的分析结果,在误差范围内具有很好的一致性。此外,对美国地质调查局提供的准标样NKT-1霞石岩（相对于IRMM-016）给出了定值,δ7Li值为（8.71±0.46）‰（2σ,n=4）。因此,本方法可用于测定天然样品的Li同位素组成。

A high-yield lithium separation technique for rock samples has been established together with precise Li isotope analysis by MC-ICP-MS.The solutions with different concentration of lithium element standard reference materials and single element standard samples of potassium,calcium,sodium,magnesium and iron were used to evaluate the analytical methods applied.Three separate stages of ion-exchange chromatography were carried out using organic cation exchange resin（AG 50W-X8,200—400 mesh）.Lithium was enriched in different eluants for the different stages.2.8 mol/L HCl,0.15 mol/L HCl and 0.5 mol/L HCl in 30% ethanol were used for the different three stages.Two kinds of columns which are made of polypropylene for the first and second stages and quartz for the third stage were used,which is different from those used abroad.Total reagent volume for the entire chemical process was reduced to 38 mL for the rock samples and the recovery is more than 97.6%.The precision of this technique is conservatively estimated to be ±0.60‰—0.94‰（2σ population）,which is similar to the precision of other methods used abroad.The δ7Li value（7Li/6Li relative to the IRMM-016 standard） determined for AGV-2 is 5.13‰.The δ7Li values determined for BHVO-2（7Li/6Li relative to the IRMM-016 standard） and IRMM-016（7Li/6Li relative to the L-SVEC standard） are 4.08‰ and 0.038‰,respectively.In addition,the results for the same kinds of samples analyzed by my lab are the same as those by isotope lab of Maryland University.All the analytical results are consistent with those reported by others.Moreover,the δ7Li value（7Li/6Li relative to the IRMM-016 standard） determined for sub-standard NKT-1 nephelinite obtained from the United States Geological Survey（USGS） is 8.71‰ and its precision is ±0.46‰.According to the experiments,it is concluded that this proposed procedure is a suitable method for determining the lithium isotopic composition of natural samples.