The total base number (TBN) is a useful indicator of how much additives are remaining in a lubricating oil. Together with other parameters, it can be used to estimate the remaining lifetime of the lubricant. For the thermometric titration, the lubricant sample is dissolved in toluene and titrated with standard 0.1 mol/L trifluoromethanesulfonic acid in acetic acid using isobutyl vinyl ether as a thermometric endpoint indicator.
