Determination of the acidity of oils using paraformaldehyde as a thermometric end-point indicator

Abstract

The determination of the acidity of oils by catalytic thermometric titrimetry using paraformaldehyde as the thermometric end-point indicator was investigated. The sample solvent was a 1:1 (v/v) mixture of toluene and 2-propanol and the titrant was 0.1 mol L-1 aqueous sodium hydroxide. Paraformaldehyde, being insoluble in the sample solvent, does not present the inconvenience of other indicators that change the properties of the solvent due to composition changes. The titration can therefore be done effectively in the same medium as the standard potentiometric and visual titration methods. The results of the application of the method to both non-refined and refined oils are presented herein. The proposed method has advantages in relation to the potentiometric method in terms of speed and simplicity.