[Pre-print] Direct mass spectrometric analysis of naphthenic acids and polycyclic aromatic hydrocarbons in waters impacted by diluted bitumen and conventional crude oil

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Issue Date
2021-04-15
Authors
Monaghan, Joseph
Richards, Larissa C.
Vandergrift, Gregory W.
Hounjet, Lindsay J.
Stoyanov, Stanislav R.
Gill, Chris G.
Krogh, Erik T.
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Abstract
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.
Description
This 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
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