The test method describes the procedure for determination of the total acid number of new and degraded polyol ester and diester based gas turbine lubricants by potentiometric titration technique. The method was validated to cover an acidity range 0.05 to 6.0 mg KOH g-1. The method may also be suitable for the determination of acidities outside of this range and for other classes of lubricant.
This document has been modified based on the results of a round robin which took place during 2013. Major modifications include use of combination electrodes and recognizing that the volume of samples available from service or laboratory tests may make using a 20 g sample size impractical for clean oils, thus a 2.5 g sample size may be used if the 20 g sample size cannot be obtained. Precision statements have been updated.