Gran's plots for end point detection in potentiometric titration of wine

Abstract
In several samples of Slovenian white wine the concentration of ethanol in extract, pH values, and total acidity were determined, as well as the densities and refractive indices. Total acidity was determined by a classical procedure which is the accepted method of the American Society of Enologists and the AOAC, i.e. the titration of wine with a strong base up to the titration "end point" at pH 8.2. In order to find the true end point, Gran's graphical procedure was employed and some examples of its practical application are illustrated. A Gran's plot converts a logarithmic response to a linear plot and it is shown that in spite of the complex wine matrix, this analytical procedure enables a precise, reproducible and accurate determination of the total acidity of wine.