Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Characterization of Oil Sand Process-Affected Water in Constructed Wetland Treatment

Abstract

The remediation of oil sand process-affected water (OSPW) generated during the bitumen extraction in the oil sand region of Canada is an area of ongoing research interest. One of the primary remediation challenges is the removal of residual complex organic compounds present in the OSPW. In the present study, the molecular constitution of OSPW from aerated and nonaerated wetland treatments were characterized in constructed wetland treatment systems. Negative-ion and positive-ion atmospheric pressure photoionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used to provide extensive molecular-level analysis of the samples. Multiple aerated and nonaerated treatment wetland systems were characterized in terms of naphthenic acids (NAs), oxy-NAs, heteroatom NAs class, and double bond equivalent (DBE) versus carbon number to evaluate their molecular composition and variability. A broad range of heteroatom compound classes with variable relative abundances were identified. The DBE versus carbon number analysis revealed different levels of transformation of the compound classes, an indicator of NA fraction compound susceptibility to transformation. The selectivity and the extent of transformation of the compound classes were a function of the wetland design. The complementarity in the heteroatom classes detected in negative-ion and positive-ion APPI FT-ICR-MS highlight the need for multiple ionization methods for more complete coverage of the distribution of components in OSPW. The detailed molecular-level information can be useful for prediction of the fate and associated toxicity of the species and also treatment efficiencies of the wetland systems.

Deciphering Dissolved Organic Matter: Ionization, Dopant, and Fragmentation Insights via Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry

“…While ESI differentiated between autochthonous and allochthonous DOM, few compositional differences between DOM from natural and impacted sources were observed (Table ). Therefore, the molecular composition of each DOM sample was investigated using positive APPI spectra (hereafter referred to as “APPI”), a method known to enhance ionization of N-containing molecules in DOM using toluene doping. , THF was also considered as a dopant since it has been shown to ionize many N- and S-containing molecules in APPI from petroleum-affected water but has not yet been applied to DOM analysis. Figure shows the overlap of all compounds ionized in ESI with toluene and THF-doped APPI for three different DOM samples.…”

“…In addition, APPI ionized fewer S-containing compounds than in ESI (SI Table S5), contrary to THF-doped petroleum. 24,25 However, a clear advantage of APPI over ESI is the number and diversity of DON and aliphatic-like compounds that were detected (SI Figure S2, Tables S1−S3, Table S5, Figure 4) revealing compositional differences between the Suwannee and Kissimmee Rivers that were indistinguishable in routine ESI analysis (Figure 3) and providing another analytical dimension to DOM analysis.…”

“…20,21 Numerous studies have utilized toluene as an APPI dopant to ionize a wide range of less polar and aromatic compounds, 21−23 petroleum. 24,25 Given the differences in ionization energy for toluene and THF (8.83 and 9.40 eV, respectively), as well as polarity (0.375 and 1.750 dipole moment, respectively), 26 the choice of dopant will likely influence the ionization, and therefore, detection of molecules within DOM samples. For instance, given the highly aromatic nature of aquatic DOM compounds, 7,11 toluene has been utilized in APPI analysis of DOM across several samples, 27−30 but still only represents a minor fraction of the total DOM with uncharacterized structures.…”

“…Positive APPI FT-ICR MS has been implemented in petroleum analysis due to its nonselective ionization and simultaneous production of both positive and negative ions. In practice, DOM ionization in APPI from direct photon absorption is poor but can be enhanced by a chemical dopant, forming both radicals and protonated ions. , Numerous studies have utilized toluene as an APPI dopant to ionize a wide range of less polar and aromatic compounds, − while other dopants such as tetrahydrofuran (THF) have displayed a high efficiency for ionizing S-containing molecules in petroleum. , Given the differences in ionization energy for toluene and THF (8.83 and 9.40 eV, respectively), as well as polarity (0.375 and 1.750 dipole moment, respectively), the choice of dopant will likely influence the ionization, and therefore, detection of molecules within DOM samples. For instance, given the highly aromatic nature of aquatic DOM compounds, , toluene has been utilized in APPI analysis of DOM across several samples, − but still only represents a minor fraction of the total DOM with uncharacterized structures.…”

Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS) peak intensity normalization for complex mixture analyses

“…The high resolution and mass accuracy of FT‐ICR‐MS have made it a preferred technique for analyzing samples that traditionally posed analytical challenges because of their high complexity. An FT‐ICR‐MS spectrum of soil or sediment organic matter, 8–13 dissolved organic matter, 14–19 petroleum, 20,21 or beverages 22,23 can contain thousands to tens of thousands of peaks with distinct m/z ratios observed across a range of masses 7 …”