Thermometric Titration – New, Fool-Proof Determination of the Total Acid Number (TAN)

No sample preparation required. Accurate results in one minute. No matrix effects and no cumbersome sensor-management necessary. Sounds too good to be true? Think again! Metrohm (Switzerland) is pleased to introduce a new method for the straightforward determination of the total acid number (TAN) in petroleum products. The new method uses automated thermometric titration and is a superior alternative to current manual and potentiometric methods. More information is provided by a technical poster.

The TAN is commonly determined by a non-aqueous titration with strong bases and defined as mg of potassium hydroxide consumed in neutralising weakly acidic substances per gram of mineral oil. The sample is dissolved in a nonaqueous solvent, often a mixture of a nonpolar hydrocarbon and an alcohol. The titrant, a strong base such as potassium hydroxide, is dissolved in the alcohol. In standard methods, endpoint detection is performed either manually using the colour change of an indicator (e.g., ASTM D 974) or instrumentally using a pH electrode (e.g.,  ASTM D 664).

Whereas manual methods suffer from the challenge of observing a faint, fading endpoint in a frequently highly coloured solution, instrumental methods using a glass-membrane pH electrode suffer from the difficulty of working in a water-free environment.

Thermometric  titration overcomes the above mentioned shortcomings. Thermometric titration uses a maintenance-free temperature sensor that requires no rehydrating and that is not plagued by annoying fouling and matrix effects. Thermometric titration gets along without any sample preparation and can be performed directly in the petroleum product with unrivaled reproducibility in approximately one minute. Results equal those obtained with potentiometric titration according to method ASTM D 664.