No abstract

The complexity of petroleum crude oils necessitates a combination of analytical techniques to gain the in-depth compositional knowledge needed to enhance oil production or develop optimal refining strategies. This study focuses on the fractionation of four Arabian crude oils through gel permeation chromatography (GPC) to obtain chemically well-defined fractions, which are then characterized in detail using atmospheric pressure photoionization Fourier transform-ion cyclotron resonance mass spectrometry, and field desorption time-of-flight mass spectrometry. GPC is found to be a valuable tool because the described methodology produces petroleum fractions with nonpolar components reproducibly separated by total alkyl chain length. While the early-eluting fractions contained large saturated compounds and small aromatic systems with extensive alkyl chains, as well as potential asphaltene material, the later-eluting GPC fractions contained molecules with a wide range of aromatic rings but very limited alkyl chains. The molecular size contribution of aromatic rings did not change the elution time of the studied petroleum components as it appears counterbalanced by non-size effects. Preliminary tandem mass spectrometry experiments revealed the presence of noncondensed aromatic rings alongside species with up to nine fused aromatic rings in the late-eluting GPC fractions, as demonstrated for S2 class species. Finally, the GPC separation was also tested on a South American crude oil sample and found to fractionate it by the same molecular criterion, i.e., total alkyl chain length, independent of the crude oil API gravity, total sulfur and nitrogen contents, or geographical origin.