Improvement of National Standard Method for Determination of Chloropropanol Esters and Glycidyl Esters in Edible Vegetable Oil

To solve the problems of low target response and complex purification process in the third method of the national standard method GB 5009.191-2016 National Food Safety Standard the Determination of Chloropropanols and Its Fatty Esters in Food, the ester bond cleavage reaction conditions, purification methods, and derivative conditions were optimized, and the method for the determination of 2-chloro-1,3-propanediol esters, 3-chloro-1,2-propanediol esters and glycidyl esters in edible vegetable oil by gas chromatography tandem mass spectrometry was proposed. The improved experimental conditions were as follows. Chloropropanol esters were hydrolyzed into corresponding chloropropanols at room temperature for 6 min with methanol solution containing 0.5 mol·L^-1 sodium methoxide. The sample was extracted twice with a mixture of methyl tert-butyl ether and ethyl acetate at a volume ratio of 8∶2 as the extraction agent. Chloropropanols were completely derivatized at 70 ℃ for 20 min with 300 μL of n-hexane solution containing 4% (volume fraction) heptafluorobutyrylimidazole as the derivative. In the improved method, the same linear ranges of the standard curves for 2-chloro-1,3-propanediol and 3-chloro-1,2-propanediol were 30-200 μg·kg^-1 (at low concentration level) and 300-3 200 μg·kg^-1 (at high concentration level), with the same detection limits of 10 μg·kg^-1. Test for recovery was made by the standard addition method, giving results in the range of 82.3%-109%, with RSDs (n=6) of the determined values less than 9.0%. This method was applied to analysis of 5 edible vegetable oil samples, and it was shown that 3-chloro-1,2-propanediol esters were detected in all 5 edible vegetable oil, with mass fraction of 209.2-783.4 mg·kg^-1. Among them, the content level of 3-chloro-1,2-propanediol esters in almond oil was relatively higher, which was a certain potential risk.