Romanczyk M., Pfutzner C.J., Tuttle S.G. (2024) Fuel, 373, art. no. 132379 DOI: 10.1016/j.fuel.2024.132379

ABSTRACT: Due to the recent increase of oil releases onto landmasses and the lack of studies exploring the compositional fate of crude oil in terrestrial environments, germane investigations are warranted. To address this concern, atmospheric pressure chemical ionization (APCI) / carbon disulfide (CS2) solvent coupled to a high-resolution orbitrap mass spectrometer was used to chemically characterize aromatic hydrocarbon molecular radical cations (M+•) derived from crude oil as a function of weathering time in a non-aqueous environment. The soft ionization attributed by APCI/CS2 and the excellent sensitivity and mass accuracy of the orbitrap enabled thorough qualitative characterization. With limited fragmentation of M+•, Kendrick Mass Defect plots were made facilitating valuable qualitative comparison of the non-weathered and weathered crude oil upon 24- and 48-hours of weathering. The non-weathered crude oil contained twelve distinct homologue ion series (i.e., ions with the same empirical formula but increase by 14 Da, a CH2 unit). Upon 24- and 48-hour weathering periods, evaporation and photooxidation induced major compositional changes for the twelve distinct ion series. Evaporation significantly influenced the compositional fate of alkylbenzenes and alkylindanes / alkyltetralins with ≤ 12 carbons in the first 24 h of weathering. Regardless of the ion series (i.e., alkylbenzenes versus alkylpyrenes), aromatic hydrocarbons with the greatest number of alkyl carbons in chain(s) attached to the aromatic core of the compounds were significantly affected by photooxidation. Overall, the average molecular weights, total carbon numbers and ring and double bond equivalence values of the M+• decreased as a function of weathering time. The compositional changes of aromatic hydrocarbons determined from this study may provide useful information for oil spill cleanup and exposure concerns.