固相微萃取—气相色谱—同位素质谱法测定天然气中微量烃类单分子氢同位素组成

Compound-specific hydrogen isotope analysis for trace hydrocarbons in natural gas by using solid phase micro-extraction coupled to gas chromatography-isotope ratio mass spectrometry

将固相微萃取技术(SPME)与气相色谱—同位素质谱(GC—IRMS)联用,通过分析涂层类型、萃取温度、萃取时间对萃取效果及化合物同位素的影响,优化操作条件,实现了天然气中微量烃类化合物单分子氢同位素的分析。实验结果表明:(1)聚二甲基硅氧烷/二乙烯基苯/碳分子筛(PDMS/DVB/CAR)对天然气中微量烃类的萃取效果最好,灵敏度高;(2)通过单因素实验,得到优化的萃取条件:萃取温度为30℃,萃取时间为60min;(3)萃取过程对同位素的影响不大,所得氢同位素组成与样品真实值偏差小于等于5‰,样品氢同位素组成未发生明显的分馏。将优化后的参数应用于天然气同位素分析,所得化合物(C_1—C_9)单体氢同位素比值标准偏差小4‰,满足实验要求,证明SPME—GC—IRMS方法的准确高效。

A new technique has been developed for on line analysis of trace hydrocarbon in natural gas using solid phase microextraction-Gas Chromatography-Isotope Ratio Mass Spectrometry（SPME-GC-IRMS）.In this study,the SPME has been introduced to achieve the enrichment of low abundance of trace hydrocarbons,which are then introduced to GC-IRMS for hydrogen isotopic analysis.The influence of method parameters,including equilibration time,extraction temperature,and the type of fiber were systematically optimized.The SPME-GC-IRMS method,fitted with polydimethylsiloxane/divinyl benzene/carbon molecular sieve（PDMS/DVB/CAR）fiber,showed good reproducibility,and the hydrogen isotopic fractionation was not observed during the extraction process.The applicability of the SPME-GCIRMS method in the low range was evaluated in a case study on natural gas sample from Jiyang Depression,Turpan-Hami Basin and Ordos Basin.The hydrogen isotope composition can be detected from C1 to C9,and for which the standard deviation（SD）was lower than 4‰for triplicate measurements.