Use of saturates/aromatics/resins/asphaltenes (SARA) fractionation to determine matrix effects in crude oil analysis by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

We have previously demonstrated the ability of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to resolve and identify the polar species found in all petroleum distillates. The ultrahigh resolving power and mass accuracy of FT-ICR MS allow for the identification of thousands of compounds in crude oils without prior chromatographic separation. Here, we compare positive-ion ESI FT-ICR mass spectra of a South American crude oil with spectra of its saturates/aromatics/resins/asphaltenes (SARA)-isolated asphaltenes, resins, and aromatics, to ascertain the effect of the other components on the relative mass spectral abundances of the polar aromatics. Saturates are unobservable by ESI. For the chosen oil, little to no signal was obtained for the asphaltenes and resins because of their mostly acidic nature. The mass distributions, heteroatom "class" distributions, "type" (rings plus double bonds) distributions, and carbon number distributions of the aromatic fraction and unfractionated crude oil were highly similar. Thus, the saturates, asphaltenes, and resins do not affect the relative abundances of polar aromatics observed by positive-ion electrospray FT-ICR MS. It is therefore not necessary to isolate the polar aromatic fraction to characterize its chemical composition in a petroleum crude oil.