HPLC-ESI-QTOF-MS as a Powerful Analytical Tool for Characterising Phenolic Compounds in Olive-leaf Extracts

Introduction Olea europaea L. leaves may be considered a cheap, easily available natural source of phenolic compounds. In a previous study we evaluated the possibility of obtaining bioactive phenolic compounds from olive leaves by pressurised liquid extraction (PLE) for their use as natural anti-oxidants. The alimentary use of these kinds of extract makes comprehensive knowledge of their composition essential. Objective To undertake a comprehensive characterisation of two olive-leaf extracts obtained by PLE using high-performance liquid chromatography coupled to electrospray ionisation and quadrupole time-of-flight mass spectrometry (HPLCESIQTOFMS). Method Olive leaves were extracted by PLE using ethanol and water as extraction solvents at 150 degrees C and 200 degrees C respectively. Separation was carried out in a HPLC system equipped with a C18-column working in a gradient elution programme coupled to ESIQTOFMS operating in negative ion mode. Results This analytical platform was able to detect 48 compounds and tentatively identify 31 different phenolic compounds in these extracts, including secoiridoids, simple phenols, flavonoids, cinnamic-acid derivatives and benzoic acids. Lucidumoside C was also identified for the first time in olive leaves. Conclusion The coupling of HPLCESIQTOFMS led to the in-depth characterisation of the olive-leaf extracts on the basis of mass accuracy, true isotopic pattern and tandem mass spectrometry (MS/MS) spectra. We may conclude therefore that this analytical tool is very valuable in the study of phenolic compounds in plant matrices. Copyright (c) 2012 John Wiley & Sons, Ltd.