【作者】 王宁；

【导师】 岑况； 孙青；

【作者基本信息】 中国地质大学(北京) ， 地球化学， 2015， 硕士

【摘要】 尿素络合法和5A分子筛法是常用的分离富集环境样品中正构烷烃的方法。尿素络合法步骤多、流程长,每部分处理流程中都可能损失部分正构烷烃,5A分子筛法受环境影响较大,两种方法对于低含量正构烷烃的回收率普遍较低。本研究通过优化尿素络合法的络合条件(尿素用量、络合反应时间、络合反应溶剂、萃取溶剂等),减小了前处理流程中正构烷烃的损失,较大幅度提高了正构烷烃的回收率,建立了尿素络合法分离-气相色谱/同位素质谱分析样品中低含量正构烷烃单体碳同位素的方法。优化的实验流程为:采用正己烷-丙酮溶解样品,加入2ml尿素-甲醇饱和溶液,放置于4℃冰箱中反应48h;制备的尿素络合物用去离子水溶解,加入正己烷后分离出有机相和水相,分别用正己烷、丙酮-正己烷萃取有机相和水相中的正构烷烃,气相色谱法(GC)测定正构烷烃含量,气相色谱-气体同位素质谱法(GC-C-IRMS)测定正构烷烃单体碳同位素。低含量中长链正构烷烃(C19~C40)的回收率达79%~104%,高于5A分子筛法和已有尿素络合法分离富集低浓度中长链正构烷烃的回收率;正构烷烃单体碳同位素的分析精度为0.09%~0.63%(1σ)。利用建立的尿素络合法分析实际样品,能大幅降低未分峰和共流出的干扰,获得良好的净化效果,提高了实际样品中低含量正构烷烃的回收率,尤其能够满足环境样品中的低含量中长链正构烷烃的单体碳同位素分析要求。更多还原

【Abstract】 Both 5 A molecular sieves and urea adduction method are used to separating straight chain from branched/cyclic hydrocarbons. However,the 5A molecular sieves method are easy to be affected by environmental factors, and the urea adduction method cause significant loss of n-alkanes during the long and complex process. The recoveries of the n-alkanes are low in environmental sample with low amount of n-alkanes for the two methods. An improved urea adduction method to separate cyclic/branched organic compounds from the linear ones with high recoveries for low concentration n-alkane samples was developed. The amount of urea, reaction solvent, reaction time of adduction and the extracting solvent during urea adduction procedure were optimized. The optimized process emploies hexane and acetone to dissolve a saturated fraction. The mixture was added to a 2ml urea-saturated methanol solution and allowed to stand for 48 h at 4℃for complete adduction. After the urea crystals were dissolved in distilled water, hexane was added into the mixture to form aquous and organic phases. The straight chain alkanes were recovered by hexane in aquous phase,and by a mixture of hexane and acetone in organic phases. The obtained n-alkanes were analysised by GC and GC-C-IRMS. The method yielded better chromatography, reduced the impact of Unresolved Complex Mixture and co-eluting components. The recoveries of C19-C40 n-alkanes ranged from 79% to 104% with a precision of 2%~6%. The accuracies of compound specific carbon isotopes of n-alkanes ranged from 0.09%-0.63%(1σ). Comparative experiments with 5A molecular sieves were conducted so as to determine the effectiveness and accurate analysis of stable carbon isotope ratios of individual nalkanes of the improved method. The higher recovery and reliably determination of the isotopic ratio shows that the improved method meets the requirement of compound specific carbon isotope analysis of n-alkanes for environmental samples with low concentration of n-alkanes.更多还原