Selective analysis of phenolic compounds in propolis by HPLC-MS/MS.

Phenolic compounds (flavonoids and phenolic acid derivatives) are major active constituents of the resinous fraction of propolis, and also represent its allergenic principles. We have developed a chromatography electrospray ionisation tandem mass spectrometry (HPLC-ESI-MS/MS) method to characterise the polyphenolic fraction of propolis rapidly and quali-quantitatively. With precursor ion scanning, selective detection of caffeic esters was easily achieved, confirming the identification of prenyl caffeate, benzyl caffeate and phenylethyl caffeate by comparison with synthetic standards. The ionisation and fragmentation behaviour of the major propolis flavonoids was rationalised and applied to selected real samples. Taken together, the results of this study show that the introduction of precursor ion analysis leads to a significant improvement in the characterisation of the phenolic fraction of propolis, paving the way to the establishment of a better quality control for this important natural remedy.