Identification of Pyrrolizidine Alkaloids in Plants by Liquid Chromatography-Mass Spectrometry.

Pyrrolizidine alkaloids (PAs) are considered as the major constituents that cause hepatoxicity in plants. PAs can be found in about 3%-5% of the world's flowering plants. Nowadays, the identification method of PAs by separation and preparation was too slow and lacked effective power. A rapid method to identify PAs in plants must be developed. Based on the fragmentation regularity, the hepatoxic PAs and nonhepatoxic PAs were characterized by liquid chromatography-mass spectrometry (LC-MS). The detailed structures of PAs in five plants were identified based on tandem mass spectrometry (MS/MS) spectrum and chemical research information. In the present study, some new fragmentation regularities of PAs have been found, such as product ions at 122, 140 and 124, 142, which have been discovered as the characteristic fragments of lactone and mono-esterase type of saturated PAs, respectively. Moreover, two product ions at 120 and 138 have been reported as the characteristic fragments of unsaturated PAs. Some of them were found in species for the first time, and some of them may be new nature product or even new compound. Finally, we classified these plants into five categories based on PAs which were identified in the present study; the result corresponded with the classification by morphology. In addition, we have found some constituents that have odd molecular weight number only in species but not in species; the detailed structures of these non-PAs constituents need penetrating study. LC-MS was rapid and sensitive method for detecting and identifying PAs in plants. Pyrrolizidine alkaloids were the toxiferous constituent of plants. In this study, we found that PAs can be used as the characteristic constituent of species.