New insights into the analysis of faradiol esters and related compounds in Calendula

In this study, the analysis of pentacyclic triterpenediol esters (e.g., faradiol esters) in Calendula officinalis (marigold) flowers by RP-HPLC-UV and RP-UHPLC-UV-MS² is discussed. The removal of carotenoids before HPLC-UV analysis has always been considered essential. However, this study demonstrates that this is unnecessary as the carotenoids do not interfere with the primary faradiol esters and the related compounds in the HPLC-UV chromatogram. Previously identified esters include the laurates, myristates and palmitates of faradiol and of three of its isomers (e.g., arnidiol, maniladiol and calenduladiol). This study tentatively identifies novel butyrates, caproates, caprylates, caprates, stearates, palmitoleates and oleates of faradiol and its isomers. These tentative identifications were performed using UHPLC coupled with triple quadrupole mass spectrometry (MS) through in-source fragments, product ion spectra (MS²) and parent ion spectra. Moreover, the product ion spectra of the faradiol isomers were compared. While similarities exist, some isomers were distinguishable.