| 微量硫化物、硫酸盐硫同位素EA-IRMS在线测试分析 |
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| 引用本文：武晓珮,范昌福,胡斌,高建飞,李延河.2020.微量硫化物、硫酸盐硫同位素EA-IRMS在线测试分析[J].地球学报,41(5):605-612. |
| DOI：10.3975/cagsb.2020.062601 |
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| 作者 | 单位 | E-mail | | 武晓珮 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室
北京大学地球与空间科学学院 | wxp92@pku.edu.cn | | 范昌福 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | tjfchangfu@163.com | | 胡斌 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | | | 高建飞 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | | | 李延河 | 中国地质科学院矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室,自然资源部同位素地质重点实验室 | |
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| 基金项目:国家自然科学基金项目(编号: 41627802; 41973022);基本科研业务费项目(编号: YYWF201710) |
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| 中文摘要:常规EA-IRMS硫同位素测试中, 硫化银(Ag2S)的需样量为0.2~1.0 mg, 硫酸钡(BaSO4)的需样量为0.35~1.5 mg, 较大的需样量已难以满足珍贵样品及微区样品的分析要求, 因此如何减少测试样品量已成为EA-IRMS测试分析工作中急需解决的问题。通过对EA-IRMS测试系统的研究发现, 在采用常规方法测试样品时, 由于初始He载气流速(100 mL/min)、进入分流接口时的流速(10 mL/min)与进入离子源时流速 (0.3 mL/min)的差异导致样品燃烧产生的目标气体中99.7%的气体被浪费, 样品的总体利用率仅有0.3%。因此如何减少样品在测试过程中的损耗, 提高样品的利用率, 从而减少需样量的关键在于缩小载气流速的差距。本实验在常规EA-IRMS测试技术基础上进行了关键改进,在元素分析仪和分流接口之间设计增加一个由六通阀和自动加热冷阱构成的装置, 自动加热冷阱可在Load模式时收集SO2气体, 六通阀在Load-Inject模式之间切换时可改变He载气流速, 通过与分流接口匹配的反吹He载气(10 mL/min)将冷阱中富集的SO2气体送入分流接口, 从而保证进入分流接口前样品燃烧产生的SO2气体全部收集。这一改进, 理论上可以将样品的利用率提高10倍, 该系统需硫量降至3~13 μg, 并且可以提高反应管的寿命, 降低清灰的频率, 提高工作效率。同时有效避免了拖尾的产生, 提高分析结果的精密度。本次微量样品实验获得的硫同位素数据与常规方法一致, 分析精度优于0.15‰(1SD), 测量值与真值的差异在0.4‰以内, 达到国际同类实验室先进水平。此外, 该方法可为微量有机碳、氮同位素EA-IRMS测试分析工作的开展提供参考经验。 |
| 中文关键词:微量样品 硫同位素 EA-IRMS 在线分析 |
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| Micro-sulfur Isotopic Measurement in Sulfide and Sulfate by Online EA-IRMS Analysis |
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| Abstract:During the conventional sulfur isotopic measurement by EA-IRMS, Ag2S and BaSO4 sample weight required for the precise analysis is 0.2~1.0 mg and 0.35~1.5 mg respectively. The sample sizes mentioned above can hardly satisfy the requirements for micro-analysis and precious samples. Moreover, it is easy to cause the sample residue in the testing system with such big sample weight, and the data cannot reflect the real result. Therefore, how to reduce the sample sizes needed for the measurement has become the major problem to be solved in the EA-IRMS testing. Through the research on the EA-IRMS system, it has been found that the sample utilization rate by conventional method is only 0.3%, and 99.7% target gas will be wasted on account of the difference between the initial He carrier gas flow rates (100 mL/min), the flow rate entering the open split (10 mL/min) and the required flow rate entering the ion source (0.3 mL/min). As a result, the key to decreasing the loss of sample and to improving the utilization rate of the sample during the testing so as to reduce the sample weight for testing is to narrow the disparity of carrier gas flow rates. In this study, the authors made a key improvement compared with the traditional EA-IRMS technology that a device is designed between the Elemental Analysis (EA) and the open split composed of a six-port valve switching the He carrier gas flow rate (10 mL/min), and the Load-Inject mode converting and a self-heated cold trap gathering the SO2 in the Load mode. After the switch of the Load-Inject mode in the system, the cryogenic SO2 gathered in the cold trap will enter into the open split through the purge of the matched back-flushing He carrier gas in order to ensure the SO2 produced by sample combustion to be collected completely. This improvement can increase the sample utilization rate by 10 times, and the sulfur amount needed for the system can be reduced to 3~13 μg theoretically. Furthermore, this improvement can also increase the testing efficiency for its extended reaction tube service life and the reduced ash cleaning frequency. At the same time, the peak-tailing can be avoided during the testing so as to improve the measurement precision. The data of sulfide (Ag2S) and sulfate (BaSO4) samples obtained by this micro-sulfur isotopic measurement are consistent with the results of the traditional method. In addition, the data analysis precision better than 0.15‰ (1SD) and the difference value between the true and the measured value within 0.4‰ have reached the advanced level of the similar international laboratories. Furthermore, such a method can provide relevant experience for micro-organic carbon and nitrogen isotopic measurements by EA-IRMS analysis. |
| keywords:micro-sample sulfur isotope EA-IRMS online analysis |
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