Acid number in lubricating oil – Determination according to ASTM D664 and IP 177

Fresh and used petroleum products may contain acidic constituents as additives or degradation products. Acid number (AN) is a measure for the relative amount of acids present express as mg KOH per g sample. Moreover, AN is used as a quality parameter of lubricating oils both for assessing the quality of new formulations and as an indicator for the degradation of such formulations during service.

The use of a pH electrode suitable for non-aqueous titrations ensures the reliable determination of the equivalence point. A flexible sleeve diaphragm facilitates the cleaning of the sensor especially after use in heavily contaminated samples, such a used engine oils. Using the right sensor greatly increases the precision and reliability of the results.

This Application Note describes the potentiometric determination of AN according to ASTM D664 and IP 177 using the Solvotrode easyClean sensor.