Structural characterization of triacylglycerols as lithiated adducts by electrospray ionization mass spectrometry using low-energy collisionally activated dissociation on a triple stage quadrupole instrument
Structural characterization of triacylglycerols as lithiated adducts by electrospray ionization mass spectrometry using low-energy collisionally activated dissociation on a triple stage quadrupole instrument
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DOI：
10.1016/s1044-0305(99)00035-5
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发表时间：
1999-07-01
影响因子：
3.2
通讯作者：
Turk, J
中科院分区：
文献类型：
--
作者：
Hsu, FF;Turk, J
我们描述了以下特征：在三重四极杆仪器上通过电喷雾电离质谱（MS）结合低能碰撞诱导解离（CAD）获得的三酰基甘油（TAG）锂化加合物的串联质谱。这些光谱可区分异构体三酰基甘油种类，并能确定每个脂肪酸取代基的质量以及取代基在甘油主链上的酯化位置。源CAD - MS2实验可确定多不饱和脂肪酸取代基中双键的位置。电喷雾电离/质谱/质谱（ESI/MS/MS）光谱包含[M + Li - (RnCO2H)]⁺、[M + Li - (RnCO2Li)]⁺和RnCO⁺等离子等，这些离子可确定脂肪酸取代基的质量。这些离子的相对丰度反映了取代基在甘油主链上的酯化位置。串联光谱还包含反映两个相邻脂肪酸残基联合消除的离子，其中一个以游离脂肪酸形式消除，另一个以α,β - 不饱和脂肪酸形式消除。这种联合损失总是涉及sn - 2取代基，这一特征为识别该取代基提供了一种可靠的方法。未观察到反映在不损失sn - 2取代基的情况下sn - 1和sn - 3取代基联合损失的碎片离子。提出了一些机制来解释锂化TAG串联质谱中主要碎片离子的形成，这些机制得到了氘标记TAG研究和源CAD - MS实验的支持。这些机制包括最初与从相邻脂肪酸的ω - 亚甲基基团夺取的一个氢原子协同消除一个游离脂肪酸，随后形成一个环状中间体，该中间体分解产生其他特征性碎片离子。通过源CAD实验确定TAG的多不饱和脂肪酸取代基中双键的位置，在该实验中，脂肪酸取代基的二锂化加合物在离子源中产生，并在碰撞池中进行CAD。在最后的四极杆中分析产物离子以获得双键位置的信息。（C）1999年美国质谱学会
We describe features of: tandem mass spectra of lithiated adducts of triacylglycerol (TAG) species obtained by electrospray ionization mass spectrometry (ms) 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 fatty acid and the other as an alpha,beta-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-MS experiments. These schemes involve initial elimination of a free fatty acid in concert with a hydrogen atom abstracted from the ol-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. (C) 1999 American Society for Mass Spectrometry.