Determination of free fatty acids in olive oils by UPHLC–MS

A simple, fast, highly efficient and direct method using ultra-performance liquid chromatography coupled to mass spectrometry has been established for the simultaneous separation, identification and quantitation of a few saturated and unsaturated fatty acids in olive oils from various countries. No sample pretreatment techniques were employed such as extraction or derivatization for the analysis of target acids from oil samples, as the oil samples were just diluted, filtered and then directly injected to the instrument. The chromatographic separations of all target fatty acids were achieved on a Hypersil Gold C18 column of particle size 1.9μm, 50×2.1mm I.D, while the gradient elution using a binary mobile phase mixture of acetonitrile and water at a flow rate of 1.5ml/min was adopted for achieving optimum separations. The identification and quantitation of target compounds was accomplished using selected ion reaction monitoring mode. The recoveries of the fatty acids were obtained higher than 89% with good validation parameters; linearity (r²>0.992), detection limit between 0.09 and 0.24μg/ml, run to run and day to day precisions with percent relative standard deviation lower than 2.4% at both low (1μg/ml) and medium (10μg/ml) concentration levels. The total content of fatty acids in each individual oils was found in the range of 472.63–7751.20μg/ml of olive oil, while oleic acid was found to be the major fatty acid among all analyzed oils with the amount 3785.94μg/ml (maximum) in Syrian olive oil. The obtained validation parameters confirm that the proposed analytical method is rapid, sensitive, reproducible and simple and it could be applied for the successful evaluation of fatty acids in various oils and other matrices. All the fatty acids were efficiently eluted in a time of less than 8min with well resolved peaks by employing the proposed method.