Quantitative determination of epoxy stearic acids derived from oxidized frying oil based on solid-phase extraction and gas chromatography

Abstract An improved preparation method based on solid phase extraction (SPE) for determination of epoxy fatty acids derived from oleic acid in frying oils was developed. A three-step separation of fatty acid methyl esters (FAMEs) by SPE on a silica gel column was proposed, and quantification by gas chromatograph with a fiame ionization detector (GC-FID) was performed. The limits of detection (LODs) of trans - and cis -epoxy stearic acid (ESA) were 6.32 and 13.09 μg/mL, respectively. And the limits of quantification (LOQs) ranged from 20.87 to 43.19 μg/mL with recoveries ranging from 89.32% to 107.08%. Good reproducibility was observed, with an intraday relative standard deviations of 0.93–2.35%, and an interday relative standard deviations of 2.44–11.68%. Results showed total levels of ESAs in different oil samples were in the range of 235.65–5916.05 mg/kg, and the contents of ESAs increased with the increase of frying time. Thus, combining the improved sample preparation method for ESAs analysis with the separation on a fused-silica capillary column using GC is highly useful for determination of ESAs in frying oils.