pg-ng级Os同位素热表面电离质谱高精度分析测试技术

随着Os同位素在地质学领域定年与示踪的广泛应用,对分析测试精度和检出限提出了更高的要求。本文利用热表面电离质谱负离子模式(NTIMS)对Os O-3进行测定,通过试剂纯化、器皿清洗等前处理步骤的优化保证了超低的化学流程空白和获得灵敏而稳定的仪器测量信号,建立了高精度pg-ng级Os同位素分析测试方法。采用逐级剥谱法扣除氧同位素干扰,采用内标迭代法按照指数规律对仪器的质量歧视效应进行校正,全流程Os空白为0.41 pg,1 pg的190Os计数约85000 cps,质量分馏系数在0.1%以内。pg级Os采用离子计数器动态跳峰扫描模式进行测量,187Os/188Os值测量精度小于在0.2%以内;ng级Os采用法拉第杯静态接收模式采集信号,187Os/188Os值测量精度在0.005%以内。经国际上Os同位素标准溶液N2、JMC以及国家一级Re-Os同位素标准物质JCBY的验证,分析精度达到了国际同类实验室先进水平。本方法具有低空白、高灵敏度、高精度的特点,可为地质学研究提供高精度Os同位素数据。

High Precise Isotopic Measurements of pg-ng Os by Negative Ion Thermal Ionization Mass Spectrometry

Higher analytical precision and lower detection limit are required in geological dating and tracing, due to the wide application of Os. In this study, high-precision determination of pg-ng Os by Negative Ion Thermal Ionization Mass Spectrometry (NTIMS) was established by reagent purification, vessel cleaning and chemical preparation to ensure the ultra-low blank and obtain sensitive and stable signals. Isobaric oxygen interferences are corrected by stepwise spectrum stripping, and mass discrimination effect is corrected by internal standard iteration. The total procedural blank of Os is 0.41 pg, the signal of 1 pg ¹⁹⁰Os is about 85000 cps, and the mass fractionation factor is less than 0.1%. Pg level of Os is measured by ion counter dynamic jumping scan mode and the measurement precision of ¹⁸⁷Os/¹⁸⁸Os is less than 0.2%. ng level of Os using Faraday cup static mode yielded the measurement precision of ¹⁸⁷Os/¹⁸⁸Os less than 0.005%. The measured value, ¹⁸⁷Os/¹⁸⁸Os=0.3361±7 (2RSD, n=9), for national reference material JCBY is identical with the certified value within uncertainty. The analysis precision meets the advanced international laboratory level. This method has the merits of low blank, high sensitivity and high accuracy, and can provide high-precision Os isotope data of geological samples.