The acid number (AN) is an important indicator of the quality and safety of insulating, transformer, and turbine oils, which usually have low AN specifications. The manual color-indicator titration method recommended by ASTM D974 can be difficult to perform, especially for colored samples.
A better alternative is to use a titrator with a photometric sensor that can automatically detect the endpoint of the titration. This ensures consistent and reliable results, which can help to monitor and control operations more effectively.
This Application Note describes how to use the Optrode photometric sensor for the fully automated determination of the AN according to ASTM D974, ISO 6618, and IP 139. The sample is titrated with alcoholic KOH solution until the p-naphtholbenzein green-brown endpoint is reached. The endpoint is determined by a break point evaluation of the titration curve, which corresponds to the color change of the endpoint described in ASTM D974.