The identification of isoparaffin components in petroleum middle fractions including kerosene and diesel fuels was investigated by gas chromatography-mass spectrometry ( GC/MS). The isodewaxing middle fraction and distilled diesel were selected as the objective sam-ples for identification. It was shown that the isoparaffin components in middle fraction were well separated with their branched alkyl substituent numbers on a capillary chromatographic column in selected ion monitoring(SIM)mode of GC/MS. The identification for C10-C24 isopar-affins was realized with the technique of GC/MS,such as the fragmentation pathways of elec-tron ionization and SIM technique,boiling point rule,published retention indices and theoreti-cal rules about component retention behavior in GC including carbon number rule etc. Finally, the retention indices for the mono-substituted,di-substituted and multi-substituted isoparaffins from C10 to C24 were presented,which could provide an overall knowledge of isoparaffin distri-bution at carbon number level in fuels. Meanwhile,the peaks that could be well resolved in each isoparaffin group were also identified,and the detailed data for about 80 C10-C21 methyl-substituted isoparaffins and isoprenoid biomarkers were also given. The results showed that in isodewaxing middle fraction studied,the mono-substituted and di-substituted isoparaffins were the main paraffins,whereas in distilled diesel studies,the mono-substituted isoparaffins and isoprenoid biomarkers were the main ones.%以石油加氢异构中间馏分及直馏柴油为研究对象,采用气相色谱/质谱联用技术对异构烷烃的分子形态进行了研究.实验表明各碳数异构烷烃组分在毛细管气相色谱柱上表现出明显的按取代基个数簇分离的现象.对异构烷烃的异构程度进行了表征,得到不同取代基个数的异构烷烃的保留指数( RI)定性表;同时根据化合物的质谱断裂规律,参考文献数据并结合碳数及沸点规律,对 73 种甲基取代的异构烷烃及 10 种生物标记的化合物单体进行了结构定性,并计算了保留指数.为在分子水平上认识航空煤油及柴油等石油中间馏分中的异构烷烃提供了基础.定性结果表明:在研究的加氢异构中间馏分中,异构烷烃主要由单取代基和二取代基的异构烷烃组成;而在直馏柴油中,单取代基异构烷烃和类异戊二烯类生物标记化合物丰度较高.
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