Determination of extra virgin olive oil acidity by FIA-titration

A direct determination of extra virgin olive oil acidity by an automated flow injection titration is proposed. The oil sample (280 μl) is directly injected, without dilution, in the carrier stream, a n-propanol solution flowing at 2 ml/min and containing potassium hydroxide 1 mM as titrant and phenolphthalein 5 10−5 M as indicator. In the mixing chamber (1.5 ml) the sample mixes and reacts with the carrier stream. By an optical fiber beam, connected to a spectrophotometer set at 562 nm, we are able to appreciate continuously the phenolphthalein absorbance (Abs) decrease. The area of the peak “ΔAbs vs. time” has a linear correlation with the logarithm of the sample acidity. Several extra virgin olive oil samples have been analysed. The correlation curve between the official (O) and proposed methods (P) is P=(0.02±0.02)+(1.02±0.03)O, with r2=0.997 and sr=0.033; the accuracy and precision, expressed as mean error and RSD, are both <5%; the number of samples analysed per hour, the solvent and the sample consumption, in comparison with the official procedure, are respectively 12–60 versus 7–8, 2–10 ml versus 100–150 ml and 0.5 ml versus 10–20 ml. These features and the simple procedure indicate how the proposed method could represent an interesting alternative to the European community official method for the determination of free fatty acids in oil.