AUTOMATED FLOW-INJECTION SPECTROPHOTOMETRIC NONAQUEOUS TITRIMETRIC DETERMINATION OF THE FREE FATTY-ACID CONTENT OF OLIVE OIL

An automated how injection titrimetric method for the determination of olive oil acidity is proposed. A 175 mu l olive oil aliquot is inject ed in a carrier stream (the titrant) of n-propanol containing 7.5 x 10 (-4) M KOH and 4.0 x 10(-5) M phenolphthalein indicator. The sample zo ne is dispersed in the titrant while flowing at 4.4 mi min(-1) through a 1.1 mi Plexiglas mixing chamber and the absorbance of the resulting mixture is continuously monitored at 562 nm, lambda(max), for the bas ic form of the indicator. The resulting negative absorbance peaks indi cate the transition base (red)-acid (colorless)-base (red) of the indi cator. Quantitation is based on peak width measurements. Peak widths o f 31.7-97 a were measured with a relative standard deviation (RSD) of < 2.1% (n = 10), and the analytical range was 0.15-8.0% (w/w) free fat ty acid content calculated as oleic acid. The sampling rate is 30-100 h(-1) while n-propanol consumption is only 3-7 mi per run. Recoveries of oleic acid from commercial olive oils ranged from 97.9 to 101.6% (m ean 99.5%). The method was applied for the determination of free fatty acid content of thirty two samples of olive oils. Results obtained by the proposed method compare well (0.3-3.6% relative difference, mean 1.5%) with those obtained by the official European Community method th at is time consuming and uses gross amounts of organic solvents. Moreo ver comparison with a Fourier transform infrared F-IR) method reveals that by using the proposed method the useful range can be extended to lower concentrations. (C) 1997 Elsevier Science B.V.