Optimization of HPLC Method for Determination of Lactulose in Liquid Milk

In order to quantify the content of lactulose in liquid milk easily and accurately,the HPLC method for determination of lactulose in liquid milk was improved. The method used stable modified amide-based chromatographic column for separation,and eluted with acetonitrile-water mobile phase for 40 minutes gradiently. The results indicated that when the injection volume was 3 μL,the resolution was 1.5,which met the chromatographic separation detection. The optimized method has been verified that lactulose has a good linear relationship in the range of 50~2500 mg/kg,(R²=0.9997),the detection limit and the quantitative limit of lactulose were 15 mg/kg and 50 mg/kg respectively. The spiked recoveries of lactulose were in the range of 90.3%~105.6%,and relative standard deviations(n=6)in the range of 3.4%~3.9%. The proposed method was used to detect 27 actual milk samples,and the results were within a reasonable range. This method was economical and accurate for the daily detection of lactulose in liquid milk.