乙酰氯-甲醇甲酯化法测定婴幼儿配方乳粉中脂肪酸含量方法的优化

目的改进乙酰氯-甲醇甲酯化气相色谱(gas chromatography,GC)法测定婴幼儿配方乳粉中脂肪酸含量的方法。方法改进了乙酰氯-甲醇配制的体积浓度,考察了不同甲酯化反应温度和时间对月桂酸、肉豆范酸、亚油酸(linoleic acid,LA)、α-亚麻酸(α-linolenic acid,α-LA)、二十二碳六烯酸(docosahexaenoic acid,DHA)和花生四烯酸(arachidonic acid,AA)含量测定的影响,并验证了改进方法的检出限、重现性和回收率等。结果采用改进的乙酰氯-甲醇配制液可将甲酯化反应时间缩短至60 min,在4℃下保存该配制液有效期达10 d。各组分在一定质量浓度范围内线性关系良好(r>0.999)。改进方法中月桂酸、肉豆蔻酸、亚油酸、α-亚麻酸、二十二碳六烯酸和花生四烯酸的检出限为0.11~0.68 mg/100 g,定量限为3.3~20.4 mg/kg,与国标方法相比定量限提升了38.2%~95.0%,回收率均在95%~105%之间,稳定性相对标准偏差为0.79%~2.59%。结论改进方法能满足婴幼儿配方乳粉中脂肪酸含量的检测。

Optimization of fatty acid content determination in infant formula milk powder by acetyl chloride-methyl alcohol esterification

Objective To improve the method for the determination of fatty acids in infant formula milk powder by acetyl chloride-methyl alcohol esterification gas chromatography(GC).Methods The volume concentration of acetyl chloride-methyl alcohol was improved.The effects of different reaction temperature and time on the determination of lauric acid,myristic acid,linoleic acid(LA),α-linolenic acid(α-LA),docosahexaenoic acid(DHA)and arachidonic acid(ARA)were investigated,the detection limit,reproducibility and recovery of the improved method were verified.Results The reaction time of Methyl esterification was shortened to 60 minutes by using the modified acyl chloride-methanol mixture,and the shelf life of the mixture was up to 10 days at 4°C.The linear relationship of each component was good within a certain range of mass concentration(r>0.999).The limits of detection of lauric acid,myristic acid,linoleic acid,α-linolenic acid,docosahexaenoic acid and arachidonic acid were0.11-0.68 mg/100 g,the limits of quantification were 3.3-20.4 mg/kg.Compared with the national standard method,the limit of quantification had increased by 38.2%-95.0%,the recovery rate is between 95%-105%,and the relative standard deviations of stability were 0.79%-2.59%.Conclusion The improved method can be used for the determination of fatty acids in infant formula milk powder.