STRUCTURAL CHARAC OF TRIACYLGLYCEROLS AS LITHIATED ADDUCTS

我们描述了锂加合物的串联质谱学特征 电喷雾电离质量法获得三酰甘油物种 低能碰撞激活解离光谱 (CAD)在三级四极仪器上。光谱 三酰甘油同分异构体物种的鉴别和允许指认 每个脂肪酸取代基的质量和甘油上的位置 取代基酯化的主链。源CAD-MS2 实验允许指定双键位置 多不饱和脂肪酸取代基。ESI/MS/MS谱图 含有[M Li-(RnCO2H)]、[M Li-(RnCO2Li)]和RnCO离子，其中 其他的，允许分配大量的脂肪酸 取代基。这些离子的相对丰度反映了 取代基酯化的甘油主链。这个 串联光谱还包含反映联合消除的离子 两个相邻的脂肪酸残基，其中一个作为游离态被消除 另一种是a，b-不饱和脂肪酸。是这样的 综合损失总是涉及sn-2取代基，这一特征 提供了一种可靠的方法来识别该取代基。碎片离子 反映了sn-1和sn-3取代基的合计损失 没有观察到sn-2取代基的损失。提出了一些方案 使串联质谱图中主要碎片离子的形成合理化 的锂化标记物，这些标记物都是由氚标记的研究所支持的 Tag和由源程序进行的CAD-MS2实验。这些计划涉及初步的 游离脂肪酸与氢原子的结合消除 从相邻脂肪酸的a-亚甲基中提取， 然后形成环状中间体，该中间体分解为 产生其他特征碎片离子。双倍的测定 TAG的多不饱和脂肪酸取代基键位置为 通过源CAD实验实现，在该实验中，双锂加合物 脂肪酸取代基在离子源中产生，并且 在碰撞单元中进行计算机辅助设计。产品离子分析在 提供双键位置信息的最终四极杆。

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.