Abstract: [Objective] This study aimed to conduct an optimization research on improving the recovery rate when determining benzoic acid and sorbic acid in fermented milk using the first method（iquid chromatography）as stipulated in“GB 5009.28—2016 Food Safety National Standard Determination of Benzoic Acid,Sorbic Acid and Saccharin Sodium in Food”. [Method] By improving the pre-treatment method for extracting fermented milk samples,the sample was weighed into a 50 mL conical centrifugal tube instead of a 50 mL volumetric flask,and then ultrasonic extraction was performed. The recovery rates of the target analytes before and after optimization were compared. [Result] After optimization,the recovery rate of the target analytes were significantly improved,with an average increase of 3.80% to 6.09%,and the repeatability test results met the requirements. [Conclusion] When using the national standard method for sample pre-treatment,after weighing the samples in a centrifuge tube and conducting ultrasonic extraction,a precipitant needs to be added for centrifugation before transferring the sample to a volumetric flasks.It is worth noting that the final volume of dilution was not included in the experiment,as it did not account for the 2 mL of ferrocyanide potassium solution and 2 mL of zinc acetate solution added.The theoretical final dilution volume should be 54 mL,but the actual calculation formula used a volume of 50 mL,which will result in a lower recovery rate result. After optimization in this study,the samples were directly weighed into a 50 mL volumetric flask,and all the pre-treatment steps were carried out in the flask. The final volume of the solution was precisely controlled at 50 mL. At the same time,in the actual calculation formula,the volume used was also 50 mL. The detection recovery rate obtained by this method was close to the theoretical value,demonstrating high accuracy and good repeatability.

Key words: liquid chromatography, fermented milk, benzoic acid, sorbic acid