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ANALYTICA CHIMICA ACTA, 1997, VOL. 351, PP. 291-297 An automated flow injection titrimetric method for the determination of olive oil acidity is proposed. A 175 ml olive oil aliquot is injected 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 zone is dispersed in the titrant while flowing at 4.4 ml min-1 through a l.l ml Plexiglas mixing chamber and the absorbance of the resulting mixture is continuously monitored at 562 nm, ëmax, for the basic form of the indicator. The resulting negative absorbance peaks indicate the transition base (red) - acid (colourless) - base (red) of the indicator. Quantitation is based on peak width measurements. Peak widths of 31.7-97 s 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 fatty acid content calculated as oleic acid. The sampling rate is 30-100 h-1 while n-propanol consumption is only 3-7 ml per run. Recoveries of oleic acid from commercial olive oils ranged from 97.9 to 101.6% (mean 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 that is time consuming and uses gross amounts of organic solvents. Moreover comparison with a Fourier transform infrared (FT-IR) method reveals that by using the proposed method the useful range can be extended to lower concentrations.
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Questions and comments to author: Dr C.A. Georgiou, cag@aua.gr |