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The saturated and aromatic hydrocarbon fractions of crude oil samples have been analyzed by using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS) and conventional gas chromatography-mass spectrometry (GC-MS). In order to investigate the consistency and discrepancy of the obtained data from the two instruments, some petroleum geochemical parameters have been compared. A comparison of 23 geochemical parameters indicates that 10 parameters are comparable from the two instruments with less than 5% deviations. Therefore, GC×GC-TOFMS is equivalent to conventional GC-MS in some geochemical parameter acquisitions. However, the other 13 parameters are discrepant, including gammacerane / αβ-hopane, Ts/Tm, 2-ethyl-naphthalene / 1-ethyl-naphthalene (ENR), (2, 6-dimethyl-naphthalene +2,7-dimethyl-naphthalene) / 1,5-dimethyl-naphthalene (DNR), etc. Furthermore, compared to GC×GC-TOFMS, some low concentration compounds could not be detected by the conventional GC-MS, which results in the missing of related geochemical data. Normally, this is caused by the limited separation power and peak capacity of the conventional GC column. Besides, the co-eluting peak integrations are also affected significantly due to the incomplete separation of the compounds. Some low concentration compounds might not be detected because of the interference from the baseline noise or from other substances. GC×GC-TOFMS prevails in compound separation against the conventional GC-MS by avoiding co-elution, which achieves more accurate and precise peak area measurement with the presence of a true baseline. So petroleum geochemical parameters obtained from the GC×GC-TOFMS are more reliable than those from the conventional GC-MS. GC×GC-TOFMS may become one of the most effective analytical tools for the oil and gas geochemical study. [ABSTRACT FROM AUTHOR]

Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOFMS) is commercially available in the 1990s, with the characteristics of large peak capacity, high resolution, high sensitivity, etc. However, its application to the petroleum and geological analyses is just emerging in China and overseas. In this research, the analytical method for petroleum aromatic fraction using GCxGC-TOFMS is set up, via the choice of the column system and optimization of setting parameters, such as temperature programming, modulation time, hot pulse time, flow rate of carrier gas, data acquisition rate and data processing. The results indicate that different polar compounds of aromatic fraction distribute as bands on structured GCxGC chromatogram. Within each band, homologous compounds appear as a roof-tile structure based on the number of substituent residues. The aromatic compounds are identified and characterized according to the GCxGC chromatogram and mass spectra. According to the polarity and the number of rings, aromatic compounds are spatially present on one chromatogram, which directly reflects the distribution characteristics of complex compounds of aromatic hydrocarbons. In addition, quantitative analysis is favored as some overlapped peaks on traditional GC-MS chromatogram have been separated completely on GCxGC. Some heterocyclic atom aromatic compounds at trace level can be clearly identified using this method, for polarity differences from other interfered aromatic compounds. The development of this method and chromatogram recognition offer petroleum geologists a practical example for the application performance of GCxGC-TOFMS. [ABSTRACT FROM AUTHOR]