Photooxidation is well known as the dominant mechanism for oxygenation of petroleum compounds for both environmental and laboratory samples. The understanding of how the three major oxygen functionalities produced interact with oil and water is essential to clean-up efforts following oil spills. High resolution mass spectrometry enables the determination of molecular formula, but it alone cannot determine functionality of these compounds. It is therefore necessary to employ separation techniques to analyze these functionalities. Here, we use two separations. The first is the Wet Silica Method which isolates interfacial material (IM) from non-interfacial material to examine the photooxidized compounds that contribute to the stabilization of emulsions. The second separation is a modified aminopropyl silica (MAPS) solid-phase extraction that isolates acids from non-acids. Fractionation with MAPS enables the examination of otherwise inaccessible mid- to high-molecular weight acids due to higher ionization efficiency of lower molecular weight acids. The use of MAPS on IM fractions enables the examination of those higher molecular weight acids that have not been examined before.<br/>We subject petroleum samples to simulated sunlight irradiation at three different time points. The photooxidized samples are then subjected to the Wet Silica Method followed by MAPS extraction for the examination of the acids within the IM fraction. Each fraction is characterized by positive and negative electrospray ionization and positive atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry to identify elemental compositions. Comparison between the preliminary data for the unfractionated and fractionated samples shows that the whole unfractionated sample does not account for large extent of oxygenation. The fractionated samples show a much wider oxygen continuum extending out to higher mass that is not present in the whole unfractionated data. Each fraction also shows higher center of double bond equivalences (DBE), indicating higher aromaticity than accessed for the unfractionated sample.

Characterization of interfacial material from photooxidized petroleum samples by fourier transform ion cyclotron resonance mass spectrometry

ACS Fall 2021

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