Determination of Total Base Number (TBN) in lubricating oils by Mid-FTIR spectroscopy (c)

A Fourier transform infrared (FTIR) spectroscopic method was developed to r apidly and quantitatively determine the Total Base Number (TBN) of hydrocar bon lubricating oils by spectroscopically measuring the COO-functional grou p of the salt produced when trifluoroacetic acid (TFA) reacts with basic co nstituents present in an oil. FTIR quantification was based on a differenti al spectrum derived from. two oil spectra collected separately, one recorde d prior to and the other after the addition of a TFA reactant solution, the first spectrum being subtracted from the second. Since the TFA/base reacti on is rapid, complete and stoichiometric, the FTIR method was found to be v ery robust and capable of reliably monitoring rela- tively small changes in TBN, with a reproducibility of +/-0.17 mg KOH/g and an accuracy of similar to +/-0.20 mg KOH/g, as determined by standard addition. The method is sim ple to execute and avoids the environmentally unfriendly solvents associate d with the ASTM wet chemical methods. Implemented with appropriate software , the determination of TBN by FTIR spectroscopy would be a simple and conve nient procedure, useful for routine condition monitoring and a significant improvement over the methods presently available.