气体中甲烷单组分的色谱—真空低温富集方法及其同位素分馏效应  

Chromatography-vacuum low temperature method of methane enrichment and isotopic fractionation in gas samples

作　　者：刘清梅 李嘉成[1,2,3] 蒋文敏 熊永强 LIU Qingmei;LI Jiacheng;JIANG Wenmin;XIONG Yongqiang(State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou,Guangdong 510640,China;CAS Center for Excellence in Deep Earth Science,Guangzhou,Guangdong 510640,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所,有机地球化学国家重点实验室,广州510640 [2]中国科学院深地科学卓越创新中心,广州510640 [3]中国科学院大学,北京100049

出　　处：《石油实验地质》2024年第3期621-629,共9页Petroleum Geology & Experiment

基　　金：国家自然科学基金项目“深层油气中甲烷团簇同位素地球化学研究”(42073065)资助。

摘　　要：甲烷(CH_(4))团簇同位素分析在气候变化、能源勘探和行星生命等领域中发挥了重要作用。样品中CH_(4)的纯度直接了影响高分辨质谱团簇同位素分析的精度和准确性。针对气样中CH_(4)组分的富集纯化难题,根据气相色谱(GC)组分分离原理,实时监测组分峰形,进一步优化了载气线速、进样量等条件。同时,通过外标法量化回收率,GC组分分析验证纯度,保证纯化的有效性。通过优化色谱—真空低温富集制备方法,确定了IBEX系统载气最佳线速为12mL/min,CH_(4)进样量需小于12 mL等实验条件,可视化GC峰形确保CH_(4)峰与相邻N_(2)干扰峰基本分离,实现了CH_(4)单组分的高纯富集。当气样中CH_(4)含量小于70%而空气含量较高时,需要进行二次纯化以提高CH_(4)纯度。讨论了5Å分子筛等吸附剂在纯化过程中可能引起CH_(4)同位素分馏的原因,并通过适当延长CH_(4)收集时间来消除5Å分子筛干扰。目前,该方法单次纯化过程约90 min,CH_(4)的回收率和纯度分别为90.1%~95.7%和97.3%~98.9%,对同位素组成(δ^(13)CVPDB和δDVSMOW、Δ^(13)CH_(3)D和Δ^(12)CH_(2)D_(2))的差异均小于质谱仪的分析误差,几乎可以忽略不计。Methane(CH_(4))clumped isotope analysis plays a crucial role in the fields of climate change,energy exploration,and planetary research.The purity of CH_(4)in samples directly affects the precision and accuracy of high-resolution mass spectrometry in clumped isotope analysis.Addressing the challenge associated with enriching and purifying CH_(4)components in gas samples,this study optimized conditions such as carrier gas line speed and sample injection volume based on the principles of gas chromatography(GC)component separation,with real-time monitoring of component peak shapes.Additionally,the recovery rate was quantified using an external standard method and purity was verified through GC component analysis to ensure the effectiveness of the purifi-cation process.By optimizing the chromatography-vacuum low-temperature enrichment preparation method,the optimal carrier gas line speed for the IBEX system was determined to be 12 mL/min,with a CH_(4)injection volume less than 12 mL.This facilitated visualization of GC peak shapes,thus ensured that the CH_(4)peak was essentially separated from the adjacent N_(2)interference peak,achieving high-purity enrichment of the CH_(4)single component.When the CH_(4)content in gas samples was less than 70%and the air content was high,secondary purification was required to improve CH_(4)purity.The causes of CH_(4)isotopic fractionation during purification using adsorbents like 5Åmolecular sieves were discussed,and extending the CH_(4)collection time was proposed to eliminate the inter-ference from the 5Åmolecular sieve.Currently,this method requires approximately 90 min for a single purifica-tion process,with CH_(4)recovery and purity ranging from 90.1%to 95.7%and 97.3%to 98.9%,respectively.The differences in isotopic composition(δ^(13)C_(VPDB)andδD_(VSMOW),Δ^(13)CH_(3)D,andΔ^(12)CH_(2)D_(2))are all less than the analytical error of the mass spectrometer,making them almost negligible.

关 键 词：甲烷 气相色谱 纯度 回收率 同位素分馏 

分 类 号：TE135[石油与天然气工程—油气勘探]