硫酸盐的氧同位素测量方法

    硫酸盐不仅是常见矿物，还是自然界少数几个具有氧同位素非质量分馏效应的矿物之一。硫酸盐矿物的氧同位素组成，特别是硫酸盐的氧同位素非质量分馏效应，可以为研究其形成过程和条件提供大量有用信息，揭示一些元素浓度甚至单个同位素比值测量无法获得的特殊作用过程。但由于硫酸盐的氧同位素分析技术难度大，这一方法在国内尚未建立起来。论文介绍了BrF5法测量硫酸盐氧同位素组成的实验装置、分析流程和测量结果。该方法是目前唯一可以同时测量硫酸盐17O/16O和18O/16O比值的方法。对BaSO4国际氧同位素标准样品NBS-127和一种BaSO4化学试剂进行了多次重复测量。测量的NBS-127国际标样的δ 18O(下标 V-SMOW)=(9.20±0.11)‰，与标准值完全一致；BaSO4化学试剂的δ 18O(下标 V-SMOW)=(14.64±0.13)‰。分析精度（标准偏差）达到0.13‰(1σ)，优于国外(0.15~0.29)‰(1σ)的水平。

    Sulfates are a sort of ordinary minerals in the supergene and endogenetic geological environment. They are among the few minerals that show mass independent fractionation of oxygen isotopes. The oxygen isotopic compositions and mass independent fractionation of sulfates can provide useful information for their formation conditions, reveal special processes that can not be acquired by element concentration or single isotope ratio measurements. This is a frontier and hot topic for isotope geochemistry study in the world. Because analytical techniques of oxygen isotopes in sulfates are very complicated, this method was not established until now in China. A traditional BrF5 fluorination method for oxygen isotope measurement of BaSO4 was established recently in our lab. The separation and purification processes for BaSO4 from sulfate-bearing samples are described in this paper. The BrF5 experimental equipment, purification technique of reagent BrF5, O2 extraction preparation from sulfates and oxygen isotope measurement are introduced. The oxygen isotope compositions of an international standard of BaSO4 NBS-127, and a chemical reagent of BaSO4 were repeatedly measured. The δ 18O(subscript. V-SMOW) values of NBS-l27 are 9.20±0.11‰, which is the same as the published standard values. The δ 18O(subscript. V-SMOW) values of the chemical reagent BaSO4 are 14.64±0.13‰. The analysis precision of oxygen isotope ratios of BaSO4 is up to 0.l3‰ (1σ), and better than 0.15~0.29‰ (1σ) reported by Wasserman (1992).