丹参水溶性多酚酸的多级串联电喷雾离子阱质谱断裂机理解析

Fragmentation Mechanisms of Phenolic Acids from Danshen in an Ion Trap by Electrospray Ionization Multi-stage Tandem Mass Spectrometry

采用多级串联电喷雾离子阱质谱(ESI-MSn)直接进样法研究了丹参水溶性成分的质谱断裂规律,重点讨论了7种主要多酚酸的质谱断裂行为。实验发现:在各类酚酸中,单体丹参素和咖啡酸主要产生碎片离子[M-H-H2O]-,且丹参素比咖啡酸更容易丢失CO2;而在二聚体中发现,丹酚酸F的特殊共轭结构导致其中性丢失CO2的几率远高于H2O,丹酚酸A、迷迭香酸和紫草酸除保留单体的质谱断裂行为,还具有自己的特征断裂方式,即丹酚酸A特征丢失丹参素,迷迭香酸中性丢失丹参素的几率远高于咖啡酸,紫草酸丢失五元环上的CO2,产生碎片m/z493.1;多聚体丹酚酸B在发生多级质谱断裂的过程中不断发生重排,最后得到稳定的具有共轭结构的碎片离子m/z321.1。上述规律为丹参水溶性成分的快速分析和鉴定提供了简便的方法。

In order to achieve effective and efficient characterization of phenolic acids in Danshen, the negative ion electrospay ionization tandem mass spectrometry （ESI-MSn） experiment was applied to investigate the structures and discuss the fragmentation pathway of phenolic acids. It was found that the ion fragment of [M-H-H2 O]^- was the characteristic fragment for the monomer danshensu and caffeic acid. The danshensu was more inclined to lose neutral fragment CO2 comparing with caffeic acid. The dimers not only kept the fragmentation pathway of their monomers, but also had their own special fragmentation pathway. Ion [M-H-C9H10O5]^- was the characteristic ion for salvianolic acid A and rosmarinic acid. The fragmentation behavior of rosmarinic acid also demonstrated that the loss of danshensu was much easier than the loss of caffeic acid. The conjugate structure of salvianolic acid F led to the preference of losing fragment CO2. As to lithospermic acid, the special pathway was the neutral loss of CO2 in the MS2 and further neutral loss of danshensu in MS3. The oligomer salvianolic acid B experienced a rearrangement during ESI-MS/MS experiment to achieve a conjugate structure. All these unusual neutral losses showed that the negative ion mode was a powerful tool for analysis of phenolic acids from Danshen.