Evaluation of major caffeic acid derivatives in Echinacea purpurea dietary supplements by HPLC with photodiode array detection and electrospray mass spectrometry

An RP-HPLC method with photodiode array detection and electrospray ionization mass spectrometry was established for the determination of major caffeic acid derivatives (caftaric acid, chlorogenic acid, cynarin, and cichoric acid) in commercial Echinacea purpurea dietary supplements. The samples were extracted with 60% methanol (3 x 15 mL) by means of sonication at room temperature. The components of interest were separated on a RP-18 chromatography column using a 20-min water-methanol-trifluoroacetic acid (TFA) gradient, identified by photodiode array detection, and further confirmed by LC-ESI-MS. The quantification was performed using external standards. The sample preparations and stability of the methanolic extracts were extensively explored. Analyses of 16 commercial E. purpurea products revealed that there is a considerable variability in the content of the caffeic acid derivatives among the products tested. The current method may serve as a valuable tool for the Quality assurance (QA)/Quality control (QC) of echinacea dietary supplements.