柱色谱分离-分子筛络合洗脱过程中正构烷烃单体碳同位素分馏研究  

Study on Specific Carbon Isotope Fractionation of n-Alkanes during Column Chromatography Separation-Molecular Sieve Complexation Adsorption

作　　者：董浩伟 赵佳玉 曾凡刚[5] 谢曼曼[1] 尚文郁[1] 王淑贤[1] 孙青[1] DONG Hao-wei;ZHAO Jia-yu;ZENG Fan-gang;XIE Man-man;SHANG Wen-yu;WANG Shu-xian;SUN Qing(National Research Center for Geoanalysis,Beijing 100037,China;Key Laboratory of Cenozoic Geology and Environment,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;School of Environment&Natural Resources,Renmin University of China,Beijing 100872,China)

机构地区：[1]国家地质实验测试中心,北京100037 [2]中国科学院地质与地球物理研究所新生代地质与环境重点实验室,北京100029 [3]中国科学院地球科学研究院,北京100029 [4]中国科学院大学,北京100049 [5]中国人民大学环境学院,北京100872

出　　处：《岩矿测试》2021年第3期349-357,共9页Rock and Mineral Analysis

基　　金：国家自然科学基金项目(41877301);中国地质调查局中国地质科学院基本科研业务费项目(CSJ201902)。

摘　　要：应用气相色谱-气体同位素质谱(GC-C-IRMS)分析正构烷烃单体碳同位素之前,需要对饱和烃样品中正构烷烃和异构烷烃进行预分离、富集,在预分离和富集过程中正构烷烃单体碳同位素是否发生分馏是高精度分析正构烷烃单体碳同位素比值(δ13C)的关键。本文以正构烷烃混合溶液为对象,利用柱色谱、5A分子筛络合、环己烷-正戊烷混合溶剂两次洗脱,GC-C-IRMS分析正构烷烃单体碳同位素,研究前处理过程中正构烷烃单体碳同位素是否发生分馏。结果表明:使用柱色谱分离前后,多数正构烷烃单体碳同位素比值相差-0.2‰~0.2‰;当5A分子筛不完全络合时,未络合的正构烷烃单体碳同位素比值偏重约0.7‰,可能发生了微弱的碳同位素分馏,但并未影响洗脱后的正构烷烃单体碳同位素比值;使用环己烷-正戊烷混合溶剂洗脱前后,碳同位素比值相差-0.2‰~0.5‰,以同样方式洗脱第二次,获得的正构烷烃单体碳同位素比值与模拟样品相差-0.3‰~0.2‰。分析不同回收率(>20%)正构烷烃的单体碳同位素比值,处理前后的差值基本在0.3‰以内,可见当正构烷烃回收率低至20%左右时,其单体碳同位素仍未发生明显分馏。柱色谱分离-5A分子筛络合-混合溶剂洗脱方法适用于回收率大于20%的正构烷烃单体碳同位素分析。BACKGROUND: Before analyzing the carbon isotopes of n-alkanes by gas chromatography-gas isotope mass spectrometry(GC-IRMS), it is necessary to pre-separate and enrich n-alkanes and isoparaffins in saturated hydrocarbon samples. Whether the carbon isotope fractionation of n-alkanes occurs is the key for the high-precision analysis of the carbon isotope ratio.OBJECTIVES: To determine isotopic fractionation characteristics for n-alkanes during column chromatography and molecular sieve separation.METHODS: Saturated hydrocarbon components were extracted with a 500 mg/3 mL SPE silica gel column using 2 mL n-pentane. After separating by a 5A molecular sieve and extracting by a mixture solvent of cyclohexane and n-pentane, n-alkanes were concentrated and analyzed by gas chromatography-combustion-isotope ratio mass spectrometry(GC-C-IRMS).RESULTS: During column chromatographic separation, the carbon isotope ratio of most n-alkanes differed from-0.2‰ to 0.2‰. When n-alkanes was not completely complexed by 5A molecular sieve, the uncomplexed alkane carbon isotope was about 0.7‰ heavier, and weak carbon isotope fractionation occured, but it did not affect the eluted n-alkanes carbon isotope ratio. Eluted with cyclohexane-n-pentane mixed solvent, the carbon isotope values before and after the elution differed from-0.2‰ to 0.5‰, and eluted in the same way for the second time, the difference between the eluted n-alkanes carbon isotope and simulate sample was between-0.3‰ and 0.2‰. Analyzing the carbon isotope ratios of n-alkanes with different recoveries(>20%), the difference between carbon isotopes of n-alkanes before and after pretreatment was within 0.3‰. It was found that when the recovery was as low as 20%, the carbon isotope ratios did not undergo significant fractionation.CONCLUSIONS: The column chromatography-5A molecular sieve adsorption and mixed solvent elution method is suitable for the analysis of carbon isotope ratios of normal alkanes, which yields a recovery greater than 20%.

关 键 词：正构烷烃单体碳同位素 碳同位素分馏 柱色谱分离 5A分子筛络合 混合溶剂洗脱 气相色谱-气体同位素质谱 

分 类 号：O628[理学—有机化学] O657.63[理学—化学]