Most oil formulations contain basic additives and detergents, designed to react with and neutralise acids,[2] preventing damage to engine parts, including corrosion of metal surfaces.
This causes an ion exchange in the outer solvated layer at the glass membrane, so a change in potential is generated which can be measured by the electrode.
[3] When the end point of the chemical reaction is reached, which is shown by an inflection point on the titration curve using a specified detection system, the amount of titrant required is used to generate a result which is reported in milligrams of potassium hydroxide equivalent per gram of sample (mg of KOH/g).
[4] A colour-indicator titration, for example using test method ASTM D974, can be carried out to indicate relative changes that occur in an oil sample during its use under oxidising conditions.
[6] An appropriate aliquot of the sample is pipetted directly into the titration vessel, and isobutyl vinyl ether and toluene solvent are added.
[6] Mid-FTIR spectroscopy can be used to rapidly and quantitatively determine the BN of hydrocarbon lubricating oils by spectroscopically measuring the carboxylate (COO-) functional group of the salt produced when trifluoroacetic acid (TFA) reacts with basic constituents present in an oil sample.