The most widely used method to determine phenolic compounds in olive fruits and leaves is reversedphase high/ultra-high performance liquid chromatography (RP-HPLC/UHPLC) coupled to UV and Mass Spectrometry (MS) . In the majority of cases, no validation results were presented, or validation was carried out using only authentic standards , one exception being the study by Bertolini et al where validation results were reported for the determination of oleuropein in an effervescent formulation using spiked placebos . In some cases, internal standards (IS) were used such as resorcinol or syringaldehyde, though at what stage the IS's were added is unclear .