ASTM D4739 for base number determination by potentiometric titration
4. Summary of Test Method
4.1 The sample is dissolved in a mixture of toluene, propanol-2-ol (isopropyl alcohol), chloroform, and a small amount of water and titrated potentiometrically with alcoholic hydrochloric acid solution. The test results of this procedure are obtained by titration mode of fixed increment and fixed time additions of the titrant. An endpoint is selected from a titration curve according to the criteria given in 13.1 and used to calculate a base number.
5. Significance and Use
5.1 New and used petroleum products can contain basic constituents that are present as additives or as degradation products formed during service. The relative amount of these materials can be determined by titrating with acids. The base number is a measure of the amount of basic substances in the oil - always under the conditions of the test. The base number is used as a guide in the quality control of lubricating oil formulations. It is also sometimes used as a measure of lubricant degradation in service. Any condemning limits must be empirically established.
