天然样品中锂的分离及其同位素比值的测定

Separation and Isotopic Determination of Lithium in Natural Samples

以锂元素标准样品和K、Na、Ca、Mg元素标准样品的混合溶液为主要研究对象,采用阳离子交换树脂AG-50W X8（0.032～0.098 mm粒径）来分离富集Li,探索不同淋洗介质（包括盐酸、硝酸以及与甲醇、乙醇的混合）对Li分离纯化的最佳效果.在对比研究的基础上,建立了一种有效分离提纯天然样品中Li的方法.用本方法分离了水体、土壤、岩石等天然样品中的Li,并用MC-ICP-MS准确测定了Li同位素组成.研究结果表明,该方法的精度在0.1‰～1.0‰,与目前文献报道的分析方法具有相似的精度.经过流程前后单元素标准Li同位素比值（δ^7Li）的比较,发现化学处理过程所产生的同位素分馏约为0.3‰,化学处理的流程空白可以忽略不计.该方法测定海水δ^7Li值为（31.6±1.0）‰,与前人的分析结果吻合.因此,本方法可用于测定天然样品中的Li同位素组成.

The solution of standard reference materials, hthium, potassium, calcium, sodium and 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（0.032 -0.098 mm）, and the optimum experimental conditions were studied. Through comparative method of different eluents, an effective separation lithium from large amounts of other metal ions can be performed quantitatively on single a column （30 cm × 0.8 cm i. d. ）. The separate method was employed to the determination of lithium in some natural samples （water, rock and soil） by the multiple collector inductively coupled plasma-mass spectrometry （ICP-MS）. The precision of all samples was 0.1%o- 1.0%0. Based on the comparison of measuring two series of our in-house standard, we found that the isotopic fractionation of the chemical procedure is less than 0.3‰, which is in the same magnitude of the outer precision （2σ）. Hence, the contribution of blank lithium to the isotopic composition of lithium in samples could be neglected. The δ^7Li value of seawater （ （31.6 ± 1.0）‰） revealed that both accuracy and precision of this procedure is consistent with that reported by others. According to the experiments, it is concluded that this proposed procedure is a suitable method for determining the lithium isotopic composition of natural samples.