Determination of Choline in Edible Oil by Column-Switching Ion Chromatography Couped with Ultrasound-Assisted Dispersive Liquid-Liquid Microextraction

100 μL of 3 mol·L^-1 HCl solution was added into 5.00 mL of edible oil sample for hydrolysis at 60 ℃ for 100 min, and ultrasound-assisted dispersive liquid-liquid microextraction was performed on the hydrolyzed sample for 6 min at 80 ℃ in a water bath. The emulsion was centrifuged at 10 000 r·min^-1 for 10 min, the upper oil phase was discarded, the lower aqueous phase was filtered through a 0.45 μm filter membrane, and then analyzed by column-switching ion chromatography. Dionex IonPac CS12A cation exchange chromatographic column (250 mm×4 mm) and Dionex IonPac CG12A cation protection column (50 mm×4 mm) were used as separation columns, with 12 mmol·L^-1 methanesulfonic acid solution as eluent, and inhibition conductivity detector was used for detection. The mass concentration of choline in soybean oil, peanut oil and linseed oil was linearly related to the corresponding peak area in the range of 0.02-2.50 mg·L^-1. The detection limits (3S/N) were between 1.58-1.99 μg·L^-1. The method was applied to determination of choline in soybean oil, peanut oil and linseed oil, giving relative standard deviations (n=5) of the measured values of intra-day and inter-day less than 7.0%, and values of recovery obtained by standard addition method were in the range of 72.0%-98.0%.