High-Resolution Mass Spec Reveals Crude Oil Weathering Dynamics

Using high-resolution orbitrap mass spectrometry (HRMS), researchers have provided new insights into the compositional changes of aromatic hydrocarbons in weathered crude oil, specifically in a non-aqueous environment.

The study, conducted by researchers in the US Naval Research Laboratory, used atmospheric pressure chemical ionization (APCI) and carbon disulfide solvent coupled to a high-resolution Orbitrap mass spectrometer to ionize and qualitatively characterize the aromatic hydrocarbons. The results revealed significant changes in composition as a function of weathering time, with evaporation and photooxidation being the primary drivers of these changes.

Over a 48-hour period, the researchers observed that the average molecular weights, total carbon numbers, and ring and double bond equivalent (RDB) values of the hydrocarbons decreased. The study identified 12 distinct homologous ion series (HIS) in the non-weathered crude oil, which showed varying degrees of susceptibility to weathering. For instance, lighter aromatic hydrocarbons with fewer carbon atoms were more prone to evaporation, while heavier, more complex hydrocarbons were more significantly affected by photooxidation.

The findings suggest that aromatic hydrocarbons with greater numbers of alkyl carbons attached to their aromatic cores are particularly vulnerable to compositional changes due to photooxidation – regardless of the presence of water. The findings are consistent with observations made in previous studies conducted in aqueous environments.

"Despite the accidental rise of oil spilled onto landmasses, less research has been dedicated to evaluating the compositional changes/fate of oil prior to its introduction into bodies of water," said lead author Mark Romanczyk in a press release. "The lack of information affords an opportunity to investigate and qualitatively characterize oil as a function of weathering time in the absence of an aqueous environment. These studies may provide highly useful information for oil spill cleanup and exposure concerns."

^{Image credit: U.S. Naval Research Laboratory}