Abstract:

Based on the LC-ESI/MSⁿ technique, the four pairs of isomers of psoralen and isopsoralen, imperatorin and isoimperatorin, neohesperidin and hesperidin, naringin and narirutin were distinguished mainly by comparison of the relative abundances of their major fragment ions. Because of the effect of the hydrogen on the C8 of psoralen, the intensity of the fragment ion formed by the loss of CO₂ was relatively increased. By comparing the abundance of the product ions formed by the loss of CO and 2CO, the isomers of psoralen and isopsoralen could be distinguished. This method can also be used to distinguish the isomers of imperatorin and isoimperatorin. Because of the different connected position between glucose and rhamnose, in the mass spectrum of neohesperidin, the relative abundances of ions at m/z 489 and 343 generated by the ring-cross cleavage of glycan were more than 10%, while in the mass spectrum of hesperidin, they were all less than 1%. This approach can also be used to distinguish the isomers of naringin and narirutin. Although the fragmentation pathways were similar, according to the tiny difference of structure, the change of relative intensity of main fragment ions could be observed and it could be used to distinguish some isomers more accurately and quickly. 

Key words: LC-MSn; Relative abundance; Isomer; Product ion; Generation opportunity