Simple quantification of phenolic compounds present in the minor fraction of virgin olive oil by LC–DAD–FLD

This paper presents the results of the study on the extraction, identification and quantification of a group of important phenolic compounds in virgin olive oil (VOO) samples, obtained from olives of various varieties, by liquid chromatography coupled to UV–vis and fluorescence detection. Sixteen phenolic compounds belonging to different families have been identified and quantified spending a total time of 25 min. The linearity was examined by establishing the external standard calibration curves. Four order linear ranges and limits of detection ranging from 0.02 to 0.6 μg mL−1 and 0.006 to 0.3 μg mL−1 were achieved using UV–vis and fluorescence detection, respectively. Regarding the real samples, for the determination of the phenolic compounds in higher concentrations (hydroxytyrosol and tyrosol) a simple liquid–liquid extraction with ethanol was used to make the sample compatible with the mobile phase. Recovery values close to 100% were obtained. However, a previous solid phase extraction with Diol cartridges was necessary to concentrate and separate the minor phenolic compounds of the main interferences. The parameters affecting this step were carefully optimized and, after that, recoveries near 80–100% were obtained for the rest of the studied phenolic compounds. Also, the limits of detection were improved 15 times. Finally, the standard addition method was carried out for each of the analytes and no matrix effect was found, so the quantification of the 16 phenolic compounds from different monovarietal VOO was carried out by using the corresponding external standard calibration plot.