A Green Potentiometric Method for Determination of the Acid Number of Oils and Fats

A green titrimetric method using potentiometry is proposed for determination of the acid number of vegetable oils and animal fats. The sample is dissolved in a water-ethanol mixture (1:1 v/v) and potentiometrically titrated with a 0.02 mol L-1 aqueous NaOH standardized solution using a glass pH combined electrode. Canola, sunflower, linseed, castor, corn and soy oils as well as swine lard, a total of twelve real samples, were analyzed. The results were compared with those from the application of the procedures AOCS Cd 3d-63 and ABNT-NBR 14448 and a green visual titrimetric method, through a statistical linear regression procedure at the 95% confidence level. No evidence for systematic differences was observed. Mean relative standard deviation for the proposed procedure was 2.7%, whereas that for the AOCS and ABNT methods 5.4% and for the visual green method 4.8%.