气相色谱-同位素比值质谱法测定天然气水合物气体单体碳氢同位素

摘要

practical applicability of different gas decomposition and collection methods (I. E. Headspace, syring and drainage), and the storage effect of different decomposed gases' storage vessels (I. E. Aluminum air bag, glass bottle with butyl rubber plug) were comparatively studied. The results indicate that the best preparation methods are vacuum headspace-decomposition and in situ storage. Good precision of δ13 C - (C1 - C3, CO2) and δD - (C1 - C3) is in the range of 0.12%e -0.23%e and 1.0%e -1.8%e with relative standard deviations (RSD, n =6) of 0.38% -0.86% and 0.62% - 1.00% , respectively. The method was successfully applied in the determination of gas isotopic compositions of natural gas hydrate-bound gases from the South China Sea, Qilian Mountain Permafrost and laboratory synthetic samples. This method is easy to operate, can be applied widely, and is suitable for the determination of isotopic compositions of hydrate-bound gases.%天然气水合物气体同位素组成数据是其气体成因、运移与积聚过程研究的重要参数.目前天然气水合物气体单体碳、氢同位素仪器分析技术主要借鉴天然气的分析方法,但对水合物气的分解、收集、储存等前处理技术缺乏系统研究.本文利用气相色谱-同位素比值质谱( GC - IRMS)技术,对比研究了顶空法、注射器法和排水法等水合物气体分解与收集方法的实用性,以及铝塑气袋和丁基橡胶塞密封的玻璃顸空瓶对分解气的储存效果.实验结果表明:在丁基橡胶塞密封的玻璃顶空瓶内真空分解且原位储存是水合物气体单体碳、氢同位素分析的最佳前处理方法.方法标准偏差为0.12‰～0.23‰ [δ13C - (C1 -C3,CO2)]、1.0‰～1.8‰ [δD-(C1- C3)];相对标准偏差(RSD,n=6)为0.38％～0.86％ [δ13C-(C1-C3,CO2)]、0.62％～1.00％ [δD-(C1 - C3)].通过对南海神狐海域、祁连山冻土区、人工合成水合物样品的分析测定,表明该方法简便实用、适用范围宽,可满足天然气水合物气体单体碳、氢同位素的分析要求.