气相色谱中温度程序和样品浓度对乳样中C18脂肪酸分离效果的影响研究

乳中C18脂肪酸的同分异构体众多且含量差异较大,导致其测定分析时分离难度较大,影响后续的鉴定和定量。为了实现乳样中C18脂肪酸的良好分离,试验比较研究了3种温度程序(175℃和150℃升温程序、170℃等温程序)和3种样品浓度(提取原液、2倍稀释液、5倍稀释液)对乳样中C18脂肪酸分离效果的影响。结果表明:(1)色谱柱温度程序影响乳中C18:1脂肪酸的分离效果:就C18:1t6~C18:1t11的分离效果而言,150℃升温程序最好,175℃升温程序最差,且150℃升温程序可以分离出C18:1c15,170℃等温程序可以很好地分离开C18:1t12/13/14和C18:1t15,而175℃升温程序仅可分离出C18:1t12/13/14;(2)3种温度程序下C18:2 c9t12、C18:2t11c15与C19:0的出峰顺序不同:170℃等温程序中,C18:2c9t12和C18:2t11c15在C19:0之后出峰,而150℃升温程序时则在C19:0之前,175℃升温程序时C19:0在两种C18:2脂肪酸之间出峰;(3)样品浓度影响乳中C18脂肪酸的分离效果:在3种温度程序下2倍稀释浓度和5倍稀释浓度均可以提高C18:1t6至C18:1t11的分离效果,且150℃升温程序下5倍稀释还可以分离出C18:1t12/13/14,但5倍稀释会造成C18:1t5、C18:2t11c15浓度过低,峰高接近基线或无法检测。综上所述,色谱柱的温度程序不仅影响乳样中C18脂肪酸的分离效果,也影响脂肪酸的出峰顺序,而样品浓度主要影响C18脂肪酸的分离效果。实际分析中,采用该研究所示提取法的2倍稀释样品、并根据试验目的采用多种温度程序相结合的方法,可实现C18脂肪酸的理想分离。

Effect of Temperature Program and Sample Concentration on the Separation of C18 Fatty Acids in Milk Samples by Gas Chromatography

The isomers of C18 fatty acids in milk are numerous and their contents vary greatly in milk fat,which makes it difficult to separate this group of fatty acids in milk samples,and it in turn influences the subsequent identification and quantification.In order to better separate the C18 fatty acids in the milk samples,this study analyzed four types of milk samples with three chromatographic temperature programs(175℃,150℃,170℃)and three sample concentrations(standard,2-fold dilution,5-fold dilution).The results showed that:(1)The chromatographic column temperature program affected the separation of C18:1 fatty acids.As to the separation of C18:1t6 to C18:1t11 isomers,150℃ temperature program was the best while 175℃temperature program was the worst.Moreover,C18:1c15 could be eluted from C18:1c9 at 150℃,while C18:1t12/13/14 and C18:1t15could be eluted at 170℃ but 175℃ could only eluted C18:1t12/13/14.(2)The eluting orders of C18:2c9t12,C18:2t11c15 and C19:0 were different under three temperature programs.Using 170℃ isothermal program,C18:2c9t12 and C18:2t11c15 were eluted after C19:0,and which were before C19:0 when 150℃temperature program was used while C19:0 was enluted between these two C18:2 isomers at 175℃.(3)Sample concentration affected C18 fatty acids separation.Under the used temperature programs,the separation of C18:1t6 to C18:1t11 isomers were improved with 2-fold diluted and 5-fold dilution samples in comparison to the original sample.Moreover,when the 5-fold diluted sample was used,C18:1t12/13/14 can also be separated at 150℃.However,the 5-fold dilution resulted in a lower resolution of C18:1t5 and C18:2t11c15,their peaks were either close to the baseline or could not be detected.In summary,the column temperature program not only affected the separation of C18 fatty acids in milk samples,but also influenced the eluting orders of these fatty acids,while the sample concentration mainly affected the separation effect of C18 fatty acids.In practical analysis,the ideal separation of C18 fatty acids can be achieved by using a 2-fold diluted sample shown in the present study and using a combination of various temperature programs according to the objective of the analysis.