Titrimetric-comparable BN results determined for in-service lubricants using quantitative FTIR spectroscopy

Abstract

A new stoichiometric FTIR Base Number (BN) method of significant utility and analytical benefit to the tribology sector has been developed, providing ASTM D4739-comparable BN results in lieu of titration in a fraction of the time. Thirty-six new/in-service oils analysed by both methods were linearly related with a between-method accuracy of ~±1.0 BN and a within-FTIR method reproducibility of ~±0.50 BN. Acid pK_a differences and the comparative similarity of the FTIR results to HCl titration are discussed, including analytical benefits. It provides a rapid means of producing quality ASTM-comparable results, taking ~1 min/sample for spectral analysis versus 30–40 min for potentiometric titration. Method protocols are best suited to an open architecture FTIR accessory but can be readily adapted to flow cell equipped FTIRs. As structured, ASTM-like results are obtained rapidly with a major analytical environmental/maintenance footprint reduction, being ideally suited for in-service lubricant or research labs analysing 20–50 samples/day.