A Visual Titration Method for the Determination of the Acid Number of Oils and Fats: a Green Alternative

A visual and green titrimetric method is proposed for the determination of the acid number of oils and fats. The sample is dissolved in a water–ethanol mixture (1:1 v/v) and titrated with a 0.02?mol L^?1 aqueous NaOH solution. Phenolphthalein is used as acid-basic indicator. Oils of canola, sunflower, linseed, castor, corn and soy as well as swine lard, a total of twelve real samples, were analyzed. The results obtained were compared with those from the application of the AOCS Cd 3d-63 method, through a statistical linear regression procedure at the 95?% confidence level and no evidence for systematic differences between the two sets of results was observed. The mean RSD (relative standard deviation ) for the proposed procedure is 4.8?%, whereas that of the official method was found to be 5.4?%.