text: Although IP Standard test methods exist, the more common methods for BN are ASTM standardised, such as the potentiometric titration for fresh oils (Test method BN ASTM D2896). A sample is typically dissolved in a pre-mixed solvent of chlorobenzene and acetic acid and titrated with standardised perchloric acid in glacial acetic acid for fresh oil samples. The end point is detected using a glass electrode which is immersed in an aqueous solution containing the sample, and connected to a voltmeter/potentiometer. 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. 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). Potentiometric titration for used oils (Test method BN ASTM D4739): a sample is dissolved in a solvent mixture of Toluene/ Propan-2-ol /Chloroform with 0.5% deionised water and then titrated with standardised alcoholic hydrochloric acid. The detection system is equivalent to the fresh oil method. The used oil method uses a less polar solvent and weaker titrant, which will not dissolve the wear metals produced during operation, hence it is more suitable to analyse used oils.