Collision-induced isomerization in tandem mass spectrometry

碰撞诱导解离(CID)是串联质谱仪(MS2)获取结构信息的一种常用方法。低能多碰撞条件是现代串联质谱计最常用的实验装置，也是大多数串联质谱计实现的。这是一种简单而敏感的方法，然而，低能CID提供的结构信息相当有限；对于小分子，MS2光谱模式往往变得相当简单，而异构体的光谱模式可能变得难以区分，因为可行的裂解途径相当有限。这种异构体可以通过使用我们的能量分辨(ER)MS2策略来区分，因为击穿图对每个异构体之间细微的结构差异引起的碎片化学的能量学变化很敏感。在CID过程中，除了热力学上的变化外，可能还隐藏着前体离子的异构化过程。例如，对香豆酸邻位和对位异构体的CID过程的计算机模拟研究表明，对位异构体的裂解涉及[M-H]-异构化为二氧化碳损失的关键中间体。提出的包括异构化过程在内的裂解机理得到了能量学的支持，这与ER-MS2实验得到的数据一致。

Collision-induced dissociation (CID) is widely available method for obtaining structural information with tandem mass spectrometry (MS2). Multiple-collision conditions under low-energy regime are the most commonly used experimental setup and implemented most of the modern tandem mass spectrometers. It's an easy and sensitive method, however, low-energy CID give rather limited structural information; MS2 spectral patterns tend to become rather simple for small molecules and spectral patterns of isomers may become indistinguishable as viable fragmentation pathways are rather limited. Such isomers could be differentiated by using our energy-resolved (ER) MS2 strategy as breakdown diagrams are sensitive to the changes in energetics of fragmentation chemistry caused by subtle structural differences between each isomers. In addition to the change in energetics, isomerization process of precursor ions may be hidden in the CID process. For example, a computer modeling study on CID process of ortho- and para-isomers of coumaric acid, which show common CO2 loss, suggested that fragmentation of para-isomer involves isomerization of [M-H]- to a key intermediate for the CO2 loss. The proposed fragmentation mechanism including the isomerization process was supported by the energetics, which was consistent to the data obtained by ER-MS2 experiments.