An automated flow-reversal injection/liquid—liquid extraction approach to the direct determination of total free fatty acids in olive oils

Abstract

A continuous liquid-liquid extraction system based on an automated, simplified single-channel flow-reversal injection mode involving no segmentation or separation unit is proposed for the direct determination of total free fatty acids (FFA) in olive oils. It relies on the reaction between the Cu 2+-pyridine complex and FFA, which takes place at the organic-aqueous interface, the Cu 2+-FFA complex (copper soap) thus formed being extracted into the organic phase during the flow-reversal process. Continuous monitoring of the organic phase at 716 nm by means of a photometer located in the middle of the injection loop provides a multi-peak absorbance-time profile representing multiple reversals in the dynamic extraction process. Total FFA can thus determined in contents from 0.01 to 1.5% (3.5 × 10 −4 − 5.3 × 10 −2, M) for oleic acid in toluene-diluted oil samples (corresponding to 0.06–9.0% of FFA for original samples) with relative standard deviations in the range 4.9–7.8% and a sampling frequency of 12 h −1. The results provided by the proposed method are in accordance with those obtained with a manual procedure and comparable to those afforded by a standard acid-base titration method after appropriate correction.