Determination of phenolic acids in palm oil samples by HPLC-UV-AD using homemade flow cell

Abstract

The concentration of phenolic acids in vegetable oils is an important criterion for the assessment of the quality of oils with regard to their freshness, the maintenance of their properties, their storage and their influence on human nutrition and health. In this study, an effective and simple method for the determination of phenolic acids in palm oil using high-performance liquid chromatography with simultaneous UV and amperometric (HPLC-UV-AD) detection was carried out. A reversed-phase C18 column was used for performing this method, and the optimal conditions were determined by isocratic elution using isopropanol/H₃PO₄ with a pH of 2.40 + 7 mmol L⁻¹ NaClO₄ (17 : 83) as the mobile phase. A homemade electrochemical flow cell with a capacity of 1.00 mL was used for end-column electrochemical detection in HPLC. The cell consisted of three electrodes: a glassy carbon working electrode, an Ag/AgCl_(KCl,sat) reference electrode and a platinum auxiliary electrode. The method was validated by external and internal calibration. The best results were obtained using o-coumaric acid as the internal standard and m-coumaric acid as the surrogate standard. The detection limits ranged between 0.019 (syringic acid) and 0.029 mg L⁻¹ (ferulic acid) for UV detection and between 0.015 mg L⁻¹ (p-coumaric acid) and 0.079 mg L⁻¹ (ferulic acid) for amperometric detection. The proposed method exhibited a good linear dynamic range (3.00–20.00 mg L⁻¹) for the analytes. The usefulness of the methodology was demonstrated by the recovery of the surrogate pattern, as this was superior to 75% using both detectors for all samples. The HPLC-UV-AD system demonstrated promising results in the analysis of phenolic acids in both these and other complex matrices.