硅酸盐和金属氧化物矿物氧同位素组成的CO_2激光氟化分析

Oxygen Isotope Analysis of Silicate and Metal Oxide Minerals by CO_2 Laser Fluorination

我室采用MIR 10型CO2 激光器 ,在一种富BrF5的氛围中使激光对硅酸盐和氧化物矿物样品加热形成O2 ,经多次纯化后用 5 的分子筛吸收 ,再直接送至气体质谱仪进行氧同位素比值测定。这个实验流程与传统方法相比的改进不仅在使用激光加热技术及样品的放置上 ,而且在直接采用O2 而不是CO2 进行质谱测定。采用O2 进行直接分析的优点不仅避免了向CO2 转化过程中的潜在同位素分馏 ,而且能够得到样品的δ1 7O值 ,因此为宇宙样品分析提供了可能。CO2 激光氟化技术的优点是所需样品量小 (可低达 1～ 2mg) ,因此能够分析微小岩石区域或单矿物晶体内的氧同位素分布。同时 ,激光可以达到非常高的温度 (>40 0 0K) ,因此能够对某些难熔矿物 (如锆石、蓝晶石、橄榄石等 )进行氧同位素分析。

MIR-10 CO 2 laser has been installed in our laboratory for oxygen isotope analysis of silicate and metal oxide minerals. Mineral samples of 1.5 to 2.5*!mg are reacted with BrF 5 by laser heating to produce O 2 gas, which is transferred to the mass spectrometer by freezing it on molecular sieve 5*! in sample tubes and thus analyzed directly. This procedure not only avoids possible isotope fractionation during the conversion of O 2 to CO 2, but also obtains both δ 18O and δ 17O values which are useful for cosmogenic samples. Advantages of our extraction line are not only the significantly decreased consumption of samples, but also the precise analysis of refractory minerals (e.g., zircon, olivine and kyanite) because of its very high heating temperatures (>4*!000*!K).