Determination of 37 Fatty Acids in Edible Oils by Atmospheric Pressure Gas Chromatography-Tandem Mass Spectrometry

The study mentioned by the title was conducted to improve the sensitivity and qualitative and quantitative effects of gas chromatography-tandem mass spectrometry for detecting various fatty acids in edible oils. Referring to GB 5009.168-2016 for sample pretreatment, 1 g of evenly mixed edible oil sample was taken, and 8 mL of methanol solution containing 2% (mass fraction) sodium hydroxide was added. The mixed solution was heated by reflux at (80±1) °C until the oil droplets disappeared. Then 7 mL of 15% (volume fraction) boron trifluoride methanol solution was added into the upper end of the reflux condenser, and the mixed solution was heated by reflux at (80±1) °C for 2 min. After cooling to room temperature, 10 mL of n-heptane was added, and the mixed solution was shaken for 2 min. Then 3 mL of saturated sodium chloride solution was added, and the mixture was settled for stratification. The 5 mL of the upper n-heptane extract was taken, and 3 g of anhydrous sodium sulfate was added. The mixture was shaken for 1 min, and settled for 5 min, and the upper solution was taken and determined by atmospheric pressure gas chromatography-tandem mass spectrometry. The 37 fatty acid methyl esters were separated on CD-2560 capillary chromatographic column under programmed temperature conditions, ionized by atmospheric pressure gas chromatography ionization source, detected in multiple reaction monitoring (MRM) mode, and quantified by external standard method. It was shown that linear relationships between the mass centrations and peak areas of 37 fatty acid methyl esters were kept in definite ranges, with correlation coefficients not less than 0.999 0, and detection limits (3S/N) in the range of 0.1-1.3 mg·kg-1. Test for recovery was made according to the standard addition method, giving recoveries in the range of 80.0%-116%, and RSDs (n=6) of the determined values were less than 10%. The proposed method was used for the analysis of five types of edible oil samples. The highest detection amount of saturated fatty acids was found in lard (54.450 7%), followed by corn oil (22.970 2%), olive oil (20.556 1%), walnut oil (11.367 4%), and rapeseed oil (9.530 8%). The highest detection amount of unsaturated fatty acids was found in rapeseed oil (90.463 0%), followed by walnut oil (88.626 8%), olive oil (79.436 0%), corn oil (77.025 0%), and lard (45.547 2%).