Complex petroleum mass spectra obtained by Fourier-transform ion cyclotron resonance mass spectrometry (FTICR MS) were successfully interpreted at the molecular level by applying principle component analysis (PCA) and hierarchical clustering analysis (HCA). A total of 40 mass spectra were obtained from 20 crude oil samples using both positive and negative atmospheric pressure photoionization (APPI). Approximately 400,000 peaks were identified at the molecular level. Conventional data analyses would have been impractical with so much data. However, PCA grouped samples into score plots based on their molecular composition. In this way, the overall compositional difference between samples could be easily displayed and identified by comparing score and loading plots. HCA was also performed to group and compare samples based on selected peaks that had been grouped by PCA. Subsequent heat map analyses revealed detailed compositional differences among grouped samples. This study demonstrates a promising new approach for studying multiple, complex petroleum samples at the molecular level.

The various components of crude oil were structurally resolved using an atmospheric-pressure solids analysis probe (ASAP) coupled with ion mobility mass spectrometry (IM-MS). An ASAP source was used to broadly fractionate compounds according to their boiling points, thereby simplifying the resulting mass spectra for easier data interpretation. The m/z-mobility plots obtained by IM-MS analysis of crude oil could be used to find the structural relationship between crude oil molecules. That was demonstrated using ion mobility mass spectra from a homologous series of compounds, differing only by the number of alkyl units, found in crude oil. The peaks from this series were linearly aligned in the plot, suggesting a continuous increase of the collisional cross section with an increase of mass values and hence the absence of significant structural differences within the series. In contrast, peaks in a homologous series differing only in the number of pendant hydrogen atoms were not linearly aligned, suggesting a discontinuous increase of the collisional cross section with an increase of mass values and hence significant structural differences due to the addition or removal of hydrogen. Cases in which a slope change was observed at three- or four-peak intervals may be related to the addition of an aromatic ring to existing structures. Overall, ion mobility mass spectrometry demonstrates a useful tool that can be used to elucidate structural relationships between molecules comprising crude oil.

In this study, the peaks observed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were correlated with properties of crude oils. The correlations were statistically analyzed and graphically presented using Circos diagrams. Numerous peaks with statistical significance (p < 0.05) correlated strongly with elemental sulfur, nitrogen, nickel, and vanadium contents. In addition, a number of peaks correlated with properties such as acidity, gravity, and weight percent of residue after atmospheric residue distillation of crude oils. The correlation agreed well with generally accepted ideas, thereby validating this approach. For example, sulfur-containing classes such as S1, S2, and NS correlated positively with sulfur content. Positive correlation denotes that the relative abundance of the peaks containing S1, S2, and NS heteroatoms increased as bulk concentrations of sulfur in the samples increased. The O2 and O4 classes of compounds, presumably with COOH functional groups, had a strong correlation with total acid number. Subsequent analyses showed some correlations had carbon number and double-bond equivalence dependence. This study clearly shows the correlation between the chemical compositions determined using FT-ICR MS and the chemical and physical properties of crude oils.

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