Modern mass spectrometry methods provide a huge benefit to saponin structural characterization, especially when combined with collision-induced dissociation experiments to obtain a partial description of the saponin (ion) structure. However, the complete description of the structures of these ubiquitous secondary metabolites remain challenging, especially since isomeric saponins presenting small differences are often present in a single extract. As a typical example, the horse chestnut triterpene glycosides, the so-called escins, comprise isomeric saponins containing subtle differences such as cis-trans ethylenic configuration (stereoisomers) of a side chain or distinct positions of an acetyl group (regioisomers) on the aglycone. In the present paper, the coupling of liquid chromatography and ion mobility mass spectrometry has been used to distinguish regioisomeric and stereoisomeric saponins. Ion mobility arrival time distributions (ATDs) were recorded for the stereoisomeric and regioisomeric saponin ions demonstrating that isomeric saponins can be partially separated using ion mobility on a commercially available traveling wave ion mobility (TWIMS) mass spectrometer. Small differences in the ATD can only be monitored when the isomeric saponins are separated with liquid chromatography prior to the IM-MS analysis. However, gas phase separation between stereoisomeric and regioisomeric saponin ions can be successfully realized, without any LC separation, on a cyclic ion mobility-enabled quadrupole time-of-flight (Q-cIM-oaToF) mass spectrometer. The main outcome of the present paper is that the structural analysis of regioisomeric and stereoisomeric natural compounds that represents a real challenge can take huge advantages of ion mobility experiments but only if increased ion mobility resolution is attainable.

中文翻译：

---

离子淌度质谱法鉴别欧洲七叶树种子中的区域异构体和立体异构体皂苷。

现代质谱方法为皂苷的结构表征提供了巨大的好处，特别是与碰撞诱导的解离实验结合使用以获得皂苷（离子）结构的部分描述时，尤其如此。然而，对这些普遍存在的次级代谢产物的结构的完整描述仍然具有挑战性，特别是因为呈现微小差异的异构皂苷通常存在于单个提取物中。作为典型的例子，七叶树三萜糖苷，即所谓的七叶皂苷，包含具有细微差异的异构体皂苷，例如侧链的顺式-反式乙烯构型（立体异构体）或糖苷配基上乙酰基的不同位置（区域异构体）。 。在本文中，液相色谱和离子迁移质谱联用已被用于区分区域异构和立体异构的皂苷。记录了立体异构和区域异构皂苷离子的离子迁移率到达时间分布（ATD），表明在市场上可买到的行波离子迁移率（TWIMS）质谱仪上，可以使用离子迁移率部分分离异构体皂苷。只有在IM-MS分析之前用液相色谱法分离出同种皂苷后，才能监测到ATD的微小差异。但是，在启用了环离子迁移率的四极杆飞行时间（Q-cIM-oaToF）质谱仪上，可以在没有任何LC分离的情况下成功实现立体异构和区域异构皂苷离子之间的气相分离。