High-performance liquid chromatography with diode array detection coupled to electrospray time-of-flight and ion-trap tandem mass spectrometry to identify phenolic compounds from a lemon verbena extract

High-performance liquid chromatography with diode array and electrospray ionization mass spectrometric detection was used to carry out the comprehensive characterization of a lemon verbena extract with demonstrated antioxidant and antiinflammatory activity. Two different MS techniques have been coupled to HPLC: on one hand, time-of-flight mass spectrometry, and on the other hand, tandem mass spectrometry on an ion-trap. The use of a small particle size C18 column (1.8 μm) provided a great resolution and made possible the separation of several isomers. The UV–visible spectrophotometry was used to delimit the class of phenolic compound and the accurate mass measurements on time-of-flight spectrometer enabled to identify the compounds present in the extract. Finally, the fragmentation pattern obtained in MS–MS experiments confirmed the proposed structures. This procedure was able to determine many well-known phenolic compounds present in lemon verbena such as verbascoside and its derivatives, diglucuronide derivatives of apigenin and luteolin, and eukovoside. Also gardoside, verbasoside, cistanoside F, theveside, campneoside I, chrysoeriol-7-diglucuronide, forsythoside A and acacetin-7-diglucuronide were found for the first time in lemon verbena.