The acid content of oils – often only present
in traces – is a quality criterion and can be
determined by thermometric titration. For example, in
mineral oils and lubricating oils the total acid number
(TAN) is determined and in edible fats and oils the
free fatty acids (FFA).
Determination of the FFA content
Thermometric titrations can be carried out conveniently
using the 859
Titrotherm from Metrohm. This titrator can, of course,
also be used for classically indicated titrations.
Dissolve the olive oil in a 1:1 mixture of toluene
and 2-propanol and add a small amount of paraformaldehyde
to achieve a better endpoint indication. Titrate with
c(KOH) = 0.1 mol/L in 2-propanol to the endpoint; the
reaction is slightly endothermic. At the endpoint, the
excess hydroxyl ions catalyze the hydrolysis of paraformaldehyde.
This strongly endothermic reaction can be seen from
the sharp bend in the titration curve. No sample preparation
is necessary.
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Food
Analysis 
