Collision-induced isomerization in tandem mass spectrometry

碰撞诱导解离（CID）是一种广泛应用于串联质谱（MS2）获取结构信息的方法。低能区多重碰撞条件是现代串联质谱仪中最常用的实验装置和实现方式。低能CID是一种简便、灵敏的方法，但其提供的结构信息相当有限；对于小分子来说，MS2光谱模式变得相当简单，而同分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。这些异构体可以通过我们的能量分辨（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能量学变化很敏感。除了能量学的变化外，前体离子的异构化过程可能隐藏在CID过程中。例如，香豆酸的邻位异构体和对异构体的CID过程的计算机模拟研究表明，对异构体的断裂涉及到[M-H]-异构化为二氧化碳损失的关键中间体。能量学支持了包括异构化过程在内的断裂机理，这与ER-MS2实验数据一致。

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.