Development and validation of a rapid and sensitive gas chromatographic method for the analysis of some phenolic compounds in vegetable oils

Abstract

A new method based on simultaneous derivatization and air-assisted liquid–liquid microextraction (AALLME) is developed for the determination of some phenolic compounds in different oils. In this method, the analytes are extracted from the oil samples by NaOH solution, then a few μL of butyl chloroformate and carbon tetrachloride are injected into the NaOH solution containing the extracted analytes, and the resulting mixture is sucked into a syringe and injected several times into a test tube with a conical base. After centrifugation of the resulting cloudy solution, the fine droplets of the organic phase containing the derivatized phenols are precipitated at the bottom of the tube. Then, 1 μL of the settled phase is injected into a gas chromatograph with flame ionization detection (GC-FID). The effects of extraction solvent type, derivatization agent and extraction solvent volumes, number of extractions and reaction time on the extraction efficiency were investigated. Under the optimum conditions, the enrichment factors (EF), extraction recoveries (ER), and enhancement factors (EnF) were high and ranged between 572–991, 60–109%, and 497–1471, respectively. The calibration graphs were linear in the concentration range of 3–10 000 μg L⁻¹. Relative standard deviations (RSD, %) for the extraction of each of the selected phenols were in the ranges of 2–4% for intra-day (n = 6) and 3–5% (n = 5) for inter-day precision for a concentration of 200 μg L⁻¹ of each analyte. Limits of detection (LOD) were in the range of 1–2 μg L⁻¹. Various oil samples, including olive oil, virgin olive oil, sunflower oil, and colza oil, were successfully analyzed by the proposed method.