反相液相色谱-质谱法使用甲酸甲胺改善甘油三酯电喷雾离子化检测灵敏度

提出使用甲酸甲胺作为新型电离增强剂改善反相液相色谱-电喷雾质谱(LC-ESI-MS)检测甘油三酯灵敏度的方法.使用反相C18色谱柱,以玉米油的异丙醇溶液为样品,选择文献中常用的异丙醇-乙腈-甲醇-水,异丙醇-乙腈流动相,在考察甲酸、乙酸、甲酸铵、乙酸铵、甲酸丁胺、甲酸二丁胺、甲酸三乙胺、甲酸二乙胺、甲酸甲胺、甲酸乙胺等不同电离增强剂的基础上,比较了甲酸甲胺和常用的甲酸铵电离增强剂对LC-ESI-MS分析甘油三酯检测灵敏度的影响,结果表明,甲酸甲胺可以使其中三亚油酸甘油酯组分的质谱峰响应值和信噪比均约为使用甲酸铵的5倍.考察了使用甲酸甲胺时,甲酸甲胺电离增强剂的浓度、流动相流速以及雾化气流速对检测的影响.通过测定不同玉米油浓度与其中甘油三酯总离子流色谱峰面积的关系曲线,显示玉米油中甘油三酯组分在不同流动相的电喷雾过程中出现聚集的最小浓度相差不大,三亚油酸甘油酯峰面积与浓度在7×10-7~2×10-4 mol/L范围内的线性关系较好,相关系数R2=0.9997,在更高的浓度时则峰面积增加缓慢.根据实验数据分析甲酸甲胺改进检测的机理,提出含有疏水性基团的加合甲胺单电荷离子具有较低的溶剂化能,在雾滴表面富集的加合甲胺离子容易被蒸发,从而提高了电喷雾离子化效率.本方法为LC-ESI-MS分析食用油中甘油三酯时提高检测灵敏度提供了有效途径.

Improvement of Detection Sensitivity of Triglyceride with Methylamine Formate as Ionization Enhancer in Reversed Phase Liquid Chromatography-Electrospray Ionization Mass Spectrometry

A novel ionization enhancer, methylamine formate, was proposed for improving the detection sensitivity of triglyceride in edible oil by reversed phase liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS).The commonly used isopropanol-acetonitrile-methanol-water and isopropanol-acetonitrile were selected as the mobile phase.By using a reversed phase C18 column, and taking the corn oil in isopropyl alcohol as sample solution, we compared methylamine formate with ammonium formate, as ionization enhancers, for their effect on the detection sensitivity of triglyceride by LC-ESI-MS after screening other different ionization enhancers, such as formic acid, acetic acid, ammonium formate, ammonium acetate, butyl formate, dibutylamine formate, triethylamine formate, diethylamine formate, methylamine formate, and ethylamine formate.The result indicated that, by using methylamine formate, the mass spectral peak response and the signal to noise ratio for trilinoleic glyceride component were 5 times higher than that of ammonium formate.The effect of the concentration of methylamine formate ionization enhancer, the flow rate of the mobile phase and the flow rate of nebulizing gas on the detection of methylamine formate were investigated.The concentration of triglyceride components in corn oil starting to form aggregates was similar in different mobile phases in the electrospray process according to measurement of the relationship between corn oil concentrations and the total ion chromatogram peak area of triglyceride.In particular, the peak area of trilinolein was linear with its concentration in the range of 7×10-7-2×10-4 mol/L (R2=0.9997), but increased slower in the higher concentration range.According to the experimental data, the mechanism for improvement of detection sensitivity of methylamine formate was suggested as that the addition of methylamine mono-charged ions with hydrophobic groups had lower solvation energy, which made the enriched addition ions easily evaporation from the droplet surface, thus improving the electrospray ionization efficiency.This method provided an effective way to improve the detection sensitivity of triglyceride in edible oil by LC-ESI-MS.