Analyzing hydrocarbon fractions in crude oils by two-dimensional gas chromatography/time-of-flight mass spectrometry under reversed-phase column system

Two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC/TOFMS) is quite effective to analyze organic compounds in crude oils with high resolution and normal-phase column condition (non-polar/polar) was commonly used. Here, to improve the understanding on this method, based on Chinese oil samples, we analyze hydrocarbon fractions in the oils using GC × GC/TOFMS with reversed-phase column system (polar/non-polar) in addition to the normal-phase column system. Results show that the reversed-phase column system is more effective in separating saturated hydrocarbons than normal-phase column system. It is especially effective in generating two-dimensional spectra, because the compounds have a higher separation among different series (polarities). The reversed-phase column system is also particularly effective in separating weakly polar to non-polar saturated hydrocarbons (e.g., branched alkanes and naphthenes of low-to-medium molecular weight). It is also suitable for the isolation and identification of conventional biomarkers such as isoprenoids, steranes, and terpanes. Overall, in the GC × GC/TOFMS analysis of crude oils, the reversed-phase system has distinct advantages over the normal-phase system and specific compounds were identified in detail. Thus, this method deserves more attention. These results and understandings add new knowledge to oil geochemistry and have general implications.