Membrane sampling separates naphthenic acids from biogenic dissolved organic matter for direct analysis by mass spectrometry

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Issue Date
2022-03-01
Authors
Duncan, Kyle D.
Hawkes, Jeffrey A.
Berg, Mykelti
Clarijs, Bas
Gill, Chris G.
Bergquist, Jonas
Lanekoff, Ingela
Krogh, Erik T.
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Abstract
Oil sands process waters can release toxic naphthenic acids (NAs) into aquatic environments. Analytical techniques for NAs are challenged by sample complexity and interference from naturally occurring dissolved organic matter (DOM). Herein, we report the use of a poly(dimethylsiloxane) (PDMS) polymer membrane for the on-line separation of NAs from DOM and use direct infusion electrospray ionization mass spectrometry to yield meaningful qualitative and quantitative information with minimal sample cleanup. We compare the composition of membrane-permeable species from natural waters fortified with a commercial NA mixture to those derived from weak anion exchange solid-phase extraction (SPE) using high-resolution mass spectrometry. The results show that SPE retains a wide range of carboxylic acids, including biogenic DOM, while permeation through PDMS was selective for petrogenic classically defined NAs (CnH2n+zO2). A series of model compounds (log Kow ∼1–7) were used to characterize the perm-selectivity and reveal the separation is based on hydrophobicity. This convenient sample cleanup method is selective for the O2 class of NAs and can be used prior to conventional analysis or as an on-line analytical strategy when coupled directly to mass spectrometry.
Description
This is a peer-reviewed accepted manuscript version of an article that was published as: Duncan, K.D., Hawkes, J.A., Berg, M., Clarijs, B., Gill, C.G., Bergquist, J., Lanekoff, I., & Krogh, E.T. (2022). Membrane sampling separates naphthenic acids from biogenic dissolved organic matter for direct analysis by mass spectrometry. Environmental Science & Technology, 56(5), 3096-3105. https://doi.org/10.1021/acs.est.1c07359
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