缬草素及其同分异构体异缬草素的电喷雾多级质谱区分

目的：对缬草素(valtrate)和异缬草素(isovaltrate)在电喷雾质谱下的裂解途径进行探讨。方法：采用高效液相色谱-电喷雾离子阱质谱对样品进行系统研究，正离子模式下进行检测，毛细管电压为3.5 kV。液相色谱条件：色谱柱为Agilent XDB-C₁₈柱(50 mm×4.6 mm，5 μm)，流动相为水-乙腈(32∶68)，流速1 mL·min^-1。结果：缬草素和异缬草素在正离子模式下，8，10位环氧结构均存在2种裂解途经：一是环氧基团(CH₂O)丢失，二是环氧基团异构化形成醛基结构；此外，由于11位取代基及7位酯基所处空间效应和诱导效应的不同使缬草素和异缬草素在正离子模式下会形成不同的特征碎片离子，如缬草素会形成m/z为219和m/z 415的特征碎片，而异缬草素会出现m/z 261和m/z 385的特征碎片。结论：该质谱检测方法可以区分同分异构体缬草素和异缬草素，并为含有环氧结构的这类环烯醚萜化合物的快速鉴定提供参考。

Objective: To study the collision-induced dissociation fragmentation pathways of valtrate and isovaltrate by ESI-MSⁿ. Methods: The samples were studied using high performance liquid chromatography-electrospray ionization tandem mass spectrometry(HPLC-ESI-MSⁿ)in positive ion mode and the capillary voltage was 3.5 kV.An Agilent XDB-C₁₈ column(50 mm×4.6 mm,5 μm)was adopted;the mobile phase was acetonitrile and water(68∶32)at a flow rate of 1 mL·min^-1. Results: The collision-induced dissociation fragmentation pathways of both compounds were described.8,10 epoxide-group of valtrate and isovaltrate had two dissociation fragmentation pathways in the positive ion mode.One pathway was the loss of the epoxide group(CH₂O),the other was the isomerization of the epoxide group to form the acetal structure.Furthermore,due to the space effect and the inductive effect of the substituent at position 11 and the ester group at position 4,different characteristic fragment ions of valtrate and isovaltrate were formed in the positive ion mode,such as the fragment ions of valtrate formed as m/z 219 and m/z 415 fragment ions,while those of isovaltrate as m/z 261 and m/z 385.Conclusion: This approach can be used to distinguish the isomers of valtrate and isovaltrate.The established method can also be used for the sensitive and rapid identification of this kind of iridoid compound with a structure of epoxide group.