Over the years, ultrahigh resolution mass spectrometry has successfully illustrated the extreme complexity of crude oil and related solubility or polarity based fractions on a molecular level. However, the applied ionization technique greatly influences the outcome and may provide misleading information. In this work, we investigate the atmospheric pressure laser ionization (APLI) technique coupled with Fourier transform ion cyclotron resonance mass spectrometer to analyze the asphaltene fraction of a crude oil. These results were compared to data obtained by using other existing atmospheric pressure ionization methods. Furthermore elemental analysis and solid state NMR were used to obtain the bulk characteristics of the asphaltene sample. The results of the different ionization techniques were compared with the bulk properties in order to describe the potential discrimination effects of the ionization techniques that were observed. The results showed that APLI expands the range of the assigned molecules, while retaining information already observed with the generally used ion sources.

In this study, a heavy crude oil sample was separated on the basis of solubility and polarity, resulting in saturates, aromatics, resins, and asphaltenes (SARA) fractions. The fractions were analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled to atmospheric pressure laser ionization (APLI). On the basis of the APLI–FT-ICR MS results, the molecular formulas and their corresponding aromaticity were compared to the bulk crude oil. The maltenes showed almost identical compound class distribution to the bulk sample, while the subfractions of the maltenes denoted unique distributions in compound classes and aromaticity. The aromaticity distributions of the fractions were in good agreement with expectations; however, the resins fraction showed higher aromaticity than the aromatics fraction. The potential of the SARA fractionation method as a sample-simplification tool that allows for a reduction of components present during the measurements was also demonstrated using APLI–FT-ICR MS