STRUCTURAL CHARAC OF TRIACYLGLYCEROLS AS LITHIATED ADDUCTS

我们描述了锂化加合物的串联质谱特征 通过电喷雾电离质谱获得的三酰基甘油物质 低能碰撞活化解离光谱法 (CAD)在三级四极杆仪器上 光谱 区分异构三酰甘油种类，并允许分配 每个脂肪酸取代基的质量和在甘油上的位置 取代基被酯化的主链。 源CAD-MS 2 实验允许分配双键位置， 多不饱和脂肪酸取代基。 ESI/MS/MS光谱 含有[M+Li-（RnCO 2 H）]+、[M+Li-（RnCO 2Li）]+和RnCO+离子， 另一些，允许分配脂肪酸的质量 取代基。 这些离子的相对丰度反映了 取代基被酯化的甘油主链。 的 串联光谱还包含反映组合消除的离子， 两个相邻的脂肪酸残基，其中一个作为游离的 脂肪酸，另一种为A，B-不饱和脂肪酸。 等 组合损失总是涉及sn-2取代基，并且该特征 提供了一种鉴定该取代基的可靠方法。 碎片离子 反映了Sn-1和Sn-3取代基的组合损失， 没有观察到Sn-2取代基的损失。 提出了方案 使串联质谱中主要碎片离子的形成合理化 的锂化TAG，这得到了氘标记的 TAG和源CAD-MS 2实验。 这些方案涉及初始 游离脂肪酸与氢原子一起消除 从相邻脂肪酸的α-亚甲基中提取， 随后形成环状中间体，其分解为 产生其他特征碎片离子。 确定双 TAG的多不饱和脂肪酸取代基中的键位置是 通过源CAD实验实现，其中 在离子源中产生脂肪酸取代基， 在碰撞室中进行CAD。 产物离子在 最后一个四极子产生关于双键位置的信息。

We describe features of tandem mass spectra of lithiated adducts of triacylglycerol species obtained by electrospray ionization mass spectrometry with low energy collisionally activated dissociation (CAD) on a triple stage quadrupole instrument. The spectra distinguish isomeric triacylglycerol species and permit assignment of the mass of each fatty acid substituent and positions on the glycerol backbone to which substituents are esterified. Source CAD-MS2 experiments permit assignment of double bond locations in polyunsaturated fatty acid substituents. The ESI/MS/MS spectra contain [M+Li-(RnCO2H)]+, [M+Li-(RnCO2Li)]+, and RnCO+ ions, among others, that permit assignment of the masses of fatty acid substituents. Relative abundances of these ions reflect positions on the glycerol backbone to which substituents are esterified. The tandem spectra also contain ions reflecting combined elimination of two adjacent fatty acid residues, one of which is eliminated as a free f att y acid and the other as an a,b-unsaturated fatty acid. Such combined losses always involve the sn-2 substituent, and this feature provides a robust means to identify that substituent. Fragment ions reflecting combined losses of both sn-1 and sn-3 substituents without loss of the sn-2 substituent are not observed. Schemes are proposed to rationalize formation of major fragment ions in tandem mass spectra of lithiated TAG that are supported by studies with deuterium-labeled TAG and by source CAD-MS2 experiments. These schemes involve initial elimination of a free fatty acid in concert with a hydrogen atom abstracted from the a-methylene group of an adjacent fatty acid, followed by formation of a cyclic intermediate that decomposes to yield other characteristic fragment ions. Determination of double bond location in polyunsaturated fatty acid substituents of TAG is achieved by source CAD experiments in which dilithiated adducts of fatty acid substituents are produced in the ion source and subjected to CAD in the collision cell. Product ions are analyzed in the final quadrupole to yield information on double bond location.