Fatty acids contain a hydrocarbon chain and a terminal carboxylate group. The hydrocarbon chain can be saturated or unsaturated. Fatty acids are synthesized not only in the cytosol, but also by oxidation of alkanes and hydroxylation of alkenes in vitro. Fatty acids are used in various branches of industry, such as rubber, detergents and comestic industries. The chemical properties of fatty acids are related to their carboxyl group. The measurement of fatty acids in plasma, serum, and foods is very important. The researchers on the extraction and determination of free fatty acids (FFAs) have been performed more than half a century. In the present study, at first the FFA in plasma was extracted by the mixture of isopropanol: heptane: 1 M H2SO4. After extraction, hepane layer that has free fatty acids was titrated with NaOH (dissolved in absolute ethanol) in the presence of thymol blue as an indicator and the concentration of FFA was calculated. In view of the fact that the lipoprotein lipases can hydrolysis triacylglycerols and release the free fatty acids, therefore, increase the content of FFA. We used Xenical as an inhibitor of lipolytic activity of lipase. The free fatty acids content in plasma was measured in the presence and absence of Xenical by titration method. The data presented in this report showed that the average of FFA concentration in the presence and absence of Xenical are 305.65 ± 50.7 and 353.27 ± 69.1 μmol/lit, respectively. These data indicated that the concentration of free fatty acids in plasma were 13% lower in the presence of Xenical than in its absence.

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