AN-H-088
Total acid number in lubricants with thermometric titration
Summary
The total acid number (TAN) is a measure of the amount of acidic compounds present in lubricants which can cause corrosion, sludge formation, and reduced performance. The determination of TAN is usually performed by potentiometric titration (ASTM D664) or photometric titration (ASTM D974). However, thermometric titration (ASTM D8045) provides a viable alternative. It is based on the temperature change of the reaction between the acid and the titrant. Thermometric titration has several advantages over conventional methods, such as its speed or maintenance-free sensor.
This Application Note describes the fully automated TAN analysis for lubricating oils. The sample is dissolved in a mixture of toluene and 2-propanol and titrated with either 0.1 mol/L or 0.01 mol/L KOH in isopropanol. Paraformaldehyde is used to indicate the endpoint of the titration.