Analytical MethodsRapid and sensitive detection of free fatty acids in edible oils based on chemical derivatization coupled with electrospray ionization tandem mass spectrometry

•Detection FFAs in oils without complicated sample purification and enrichment was developed.•The derivative reagent (DEEA) can selectively label carboxyl group of FFA to form amino compounds.•The labeling reaction can be carried out within 5 min under mild conditions with high specificity.•The detection sensitivityof FFAs was significantly enhancedafter derivatization.•TheNLS-ESI-MS/MS method was applied to determine dynamic FFA formation in edible oils.

In this study, a strategy based on chemical derivatization coupled with electrospray ionizationtandem quadrupole mass spectrometry (ESI-MS/MS) for rapid and sensitive detection of FFAs in edible oils was developed. A derivative reagent (N,N-diethyl-1,2-ethanediamine, DEEA) was employed to selectively label carboxyl groups of FFAs to form an amino compound with a tertiary amino group. The DEEA derivative products could lose a characteristic neutral loss fragment of 73 Da in collision-induced dissociation (CID), which enabled to discriminate and analyze the DEEA derived FFAs with neutral loss scan (NLS 73 Da)under the positive ion mode of mass spectrometry. The assay was linear over the concentration range 0.5-200 nmol/L with satisfactory correlation coefficients (R2 ≥ 0.9942), whilst the limit of detection and quantitation were 0.1-0.3 nmol/L and 0.3-1.0 nmol/L, respectively. Finally, the established method was applied to determine dynamic FFA formation in seven types of edible oils subjected to a microwave heating treatment test.