Evaluations of weathering of polar and nonpolar petroleum components in a simulated freshwater–oil spill by Orbitrap and Fourier transform ion cyclotron resonance mass spectrometry

Abstract

The comprehensive chemical characterization of crude oil is important for evaluation of the transformation and fate of components in the environment. Molecular-level speciation of naphthenic acid fraction compounds (NAFCs) was investigated in a meso-scale spill tank using both negative-ion electrospray ionization (ESI) Orbitrap mass spectrometry (MS) and positive-ion atmospheric pressure photoionization Fourier transform-ion cyclotron resonance mass spectrometry (APPI-FT-ICR-MS). Both ionization techniques are coupled to high-resolution mass spectrometric detectors (ESI: Orbitrap MS; APPI: FT-ICR MS at 9.4 tesla), enabling insight into the behavior and fate of petrogenic compounds during a simulated freshwater crude oil spill. Negative-ion ESI Orbitrap-MS reveals that oxygen-containing (O_x) classes are detected early in the spill, whereby species with more oxygen per molecule evolve later in the simulated spill. The O₂-containing species gradually decreased in relative abundance while O₃ and O₄ species increased in relative abundance throughout the simulated spill, which could correspond to a relative degree of oxygen incorporation. Nonpolar speciation by positive-ion APPI 9.4 tesla FT-ICR-MS allowed for the identification of water-soluble nonpolar and less polar acidic species. Molecular level graphical representation of elemental compositions derived from simulated spill water-soluble and oil-soluble species suggest that biological activity is the primary degradation mechanism, and that biodegradation was the dominant mechanism based on an the negative-ion ESI Orbitrap-MS results.