Direct mass spectrometric analysis of naphthenic acids and polycyclic aromatic hydrocarbons in waters impacted by diluted bitumen and conventional crude oil
Richards, Larissa C.
Vandergrift, Gregory W.
Hounjet, Lindsay J.
Stoyanov, Stanislav R.
Gill, Chris G.
Krogh, Erik T.
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The accidental release of hydrocarbons has well-documented, deleterious impacts on the hydrosphere. There are several classes of toxic petroleum derived compounds, such as naphthenic acids (NAs) and polycyclic aromatic hydrocarbons (PAHs), which may present a contamination hazard in the event of an oil spill. We examine the aqueous-phase concentrations of these trace contaminants using a direct sampling, on-line, rapid screening technique known as condensed-phase membrane introduction mass spectrometry (CP-MIMS). Water samples having a range of pH and salinity were equilibrated with either diluted bitumen (DB) or conventional crude (CC) oil. CP-MIMS is employed to directly measure concentrations and isomer class profiles of classical NAs in the aqueous phase using electrospray ionization in negative-ion mode as [M-H]–. Aqueous PAH concentrations are monitored using CP-MIMS coupled to liquid electron ionization (LEI) source in positive-ion mode using selected ion monitoring (SIM) of the molecular ion (M+•). Aqueous NA concentrations are observed to be highly pH-dependent, and are an order of magnitude greater in water samples contaminated with DB compared to CC. Conversely, aqueous concentrations of naphthalene and alkyl-naphthalenes are found to be greater in water samples exposed to CC. Principal component analysis of data generated from CP-MIMS for the NA profile in the aqueous phase enables discrimination of DB and CC as contaminant sources. In addition, we describe the use of online membrane sampling for real-time, direct detection of NAs and PAHs in the same sample. These compound classes are distinguished by both their perm-selectivity behaviour at the membrane and the ionization mode at the instrument. The in-situ analysis of trace organics in water with a simple workflow described here lays the foundation for applications of direct mass spectrometry to rapid screening of large sample sets and monitoring of aqueous-phase contamination and remediation processes in real-time.
DescriptionThis document is a pre-copyedited, author-provided manuscript version of a published work that after revisions following peer review and technical editing by the publisher appeared in final form as: Monaghan, J., Richards, L.C., Vandergrift, G.W., Hounjet, L.J., Stoyanov, S.R., Gill, C.G., & Krogh, E.T. (2021). Direct mass spectrometric analysis of naphthenic acids and polycyclic aromatic hydrocarbons in waters impacted by diluted bitumen and conventional crude oil. Science of the Total Environment, 765, 1-10. To access the final edited and published work see: http://doi.org/10.1016/j.scitotenv.2020.144206
Identifier (Other)DOI: 10.1016/j.scitotenv.2020.144206