Direct quantitation and characterization of fatty acids in salmon tissue by condensed phase membrane introduction mass spectrometry (CP-MIMS) using a modified donor phase


Existing mass spectrometric methods for the analysis of fatty acids often require derivatization, chromatographic separations, and/or extensive sample preparation. Direct mass spectrometry strategies can avoid these requirements, but may also suffer from poor quantitation and/or lack of sensitivity. Condensed phase-membrane introduction mass spectrometry (CP-MIMS) provides direct quantitative measurements of analytes in complex samples with little or no sample preparation. CP-MIMS uses a semipermeable membrane to transfer neutral, hydrophobic compounds from real-world samples to a mass spectrometer. The results presented utilize aqueous/organic sample solvent (donor) mixtures to allow for the sensitive (pptr) detection of a range of fatty acids. The relative sensitivity across a homologous series of fatty acids is observed to change, favoring short- or long-chain fatty acids, depending on the amount of miscible co-solvent added to the donor phase. Further, lithium acetate added online via the acceptor phase was used in tandem mass spectrometry experiments to determine the location of double bonds in polyunsaturated fatty acids (PUFAs). The method was applied to direct measurements and structural determinations for selected PUFAs in salmon tissue samples. Standard addition was employed to quantify the amount of PUFAs in a variety of salmon samples, yielding 0.27–0.42 and 0.40–0.84 w/w % for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), respectively, for Sockeye and Chinook salmon, in good agreement with the literature. This work presents, to our knowledge, the first use of CP-MIMS for the direct analysis of fatty acids in oily foodstuff samples.

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The authors would like to acknowledge the AERL group members Heather Wilson for her contributions to this project as well as Lukas Miner, and Darien Degroot. The authors acknowledge Vancouver Island University and the University of Victoria for their ongoing support of our research. The authors acknowledge technical support for the Q-Sight MS system graciously provided by PerkinElmer.


This study was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) (Grant # RGPIN-2016-05380 CGG and RGPIN-2016-06454 ETK) and additional funding was provided by the Canada Foundation for Innovation and BC Knowledge Development Fund (CFI #32238).

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Correspondence to Chris G. Gill.

Ethics declarations

All fish samples used for this research were obtained as “food” items, and not specifically raised or collected for the purposes of this research. This includes the sport caught Chinook salmon, which was legally obtained as food by fly fishing using a BC Non-Tidal Angling Licence with the appropriate Non-Tidal Salmon Fishing Stamp.

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The authors declare that they have no conflict of interest.

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Borden, S.A., Damer, H.N., Krogh, E.T. et al. Direct quantitation and characterization of fatty acids in salmon tissue by condensed phase membrane introduction mass spectrometry (CP-MIMS) using a modified donor phase. Anal Bioanal Chem 411, 291–303 (2019).

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  • Long-chain fatty acids
  • Membrane introduction mass spectrometry
  • Salmon
  • Direct mass spectrometry
  • Omega-3 fatty acids
  • Fatty acid aggregation