金刚烷类化合物在原油及烃源岩中被广泛检出。由于其较好的热稳定性和抗生物降解能力,金刚烷参数通常被用作高成熟原油及烃源岩的成熟度评价指标。传统的分析方法主要是采用气相色谱/质谱(GC-MS)方法测定金刚烷类化合物。本研究发现在测定较低含量的金刚烷类化合物的原油样品时,一些金刚烷类化合物的GC-MS谱图与相应的金刚烷类化合物的标样存在很大的差别,明显存在其他物质共溢出的干扰。另外,由于不同金刚烷化合物的相对响应因子差别明显,使得传统的定量方法(假定不同金刚烷化合物具有相同的相对响应因子)存在较大的误差。气相色谱/质谱/质谱具有较高的选择性,因而在金刚烷类化合物的定量分析中具有较高的灵敏度和准确度。通过对金刚烷类化合物标准样品以及塔里木盆地的两个原油样品的GC-MS-MS与GC-MS对比研究发现,GC-MS-MS方法能排除基质对金刚烷类化合物的干扰,能够得到更准确的金刚烷指标;且其简单的样品前处理程序对样品产生的影响较小,是一种较好的检测原油或烃源岩中金刚烷类化合物的定量方法。
Diamondoid hydrocarbons are commonly detected in crude oils and source rocks.Due to high resistance to thermal and biological destruction,the diamondoid indices are usually used to evaluate the maturity of crude oils or source rocks.GC-MS is a traditional technique to analyze diamondoid hydrocarbons.Here we found that mass spectrums of some diamondiods in crude oils are different with those of the corresponding diamondiod standards,indicating co-elution with other compounds.In addition,when the traditional quantitative method is used for quantitation of diamondoids,distinct response factors of different diamondoid compounds probably result in large errors,assuming different diamondoids have the same response factor with its internal standard compound.GC-MS-MS has higher accuracy and sensitivity than GC-MS because of its relatively high selectivity.Comparative study of GC-MS-MS and GC-MS on the determination of diomandoid standards and two crude oils from the Tarim Basin,China,shows that the GC-MS-MS method can eliminate the disturbance of co-elution and avoid influence from complicate sample preparation procedures.Therefore,GC-MS-MS technique is a promising method for the determination of diamondoids in crude oils.