银离子固相萃取-气相色谱法检测乳脂肪中的反式脂肪酸

Determination of trans fatty acid C18∶1,C18∶2 and C18∶3 isomers in milk fat by silver ion solid phase extraction-gas chromatography

建立了分离反式油酸(C18∶1)、亚油酸(C18∶2)、亚麻酸(C18∶3)的银离子固相萃取-气相色谱(Ag+-SPE/GC)方法,并应用于乳脂肪中反式脂肪酸的检测。采用自制的银离子固相萃取柱对样品进行预分离,总脂肪酸甲酯化后上样,依次经9mL甲苯-正己烷(体积比5∶95)、8mL甲苯-正己烷(体积比17∶83)、6mL甲苯-乙酸乙酯(体积比17∶83)、10mL甲苯-乙酸乙酯(体积比30∶70)洗脱并分别收集洗脱液,采用气相色谱分别进行检测。结果显示,除了反式亚麻酸的回收率为69.9%～101.0%、相对标准偏差(RSD)为11.0%～18.1%外,其余的反式脂肪酸的回收率均为88.4%～107.2%、RSD为1.2%～11.9%。该方法通过特异性固相萃取的方法对样品进行前处理,较好地避免了样品中顺式及饱和脂肪酸对反式脂肪酸检测的干扰。

A method for the determination of trans fatty acids C18∶1,C18∶2 and C18∶3 in milk fat was developed by silver ion solid phase extraction-gas chromatography（Ag＋-SPE/GC）.The fatty acid methyl esters derived from total milk fat were loaded onto an Ag＋-SPE cartridge,and then eluted with 9 mL of toluene-hexane（5∶95,v/v）,8 mL of toluene-hexane（17∶83,v/v）,6 mL of toluene-ethyl acetate（17∶83,v/v） and 10 mL of toluene-ethyl acetate（30∶70,v/v） in sequence.The fraction from each step was analyzed by GC.The average recoveries of trans fatty acids ranged from 88.4% to 107.2% with the relative standard deviations（RSDs） from 1.2% to 11.9% except trans linolenic acid with the recoveries from 69.9% to 101.0% and the RSDs from 11.0% to 18.1%.Comparing with the traditional methods,the developed approach can avoid the interference of cis and saturated fatty acids.The method was successfully applied to analyze dairy products.Satisfactory results were shown.