ASTM D2896 for base number of petroleum products
ASTM D2896 for base number of petroleum products by potentiometric perchloric acid titration
4. Summary of Test Method
4.1 The sample is dissolved in an essentially anhydrous mixture of chlorobenzene and glacial acetic acid and titrated with a solution of perchloric acid in glacial acetic acid using potentiometric titrimeter. A glass indicating electrode and a reference electrode are used, the latter being connected with the sample solution by means of a salt bridge. The meter readings are plotted against the respective volumes of titrating solution, and the end point is taken at the inflection in the resulting curve.
4.2 Procedure A uses 120 mL of titration solvent. Procedure B uses 60 mL of titration solvent. In addition, the two procedures use different equations for the calculation of appropriate sample weights. Since many portions of the test method are identical for Procedures A and B, only the unique sections will be described separately for the two versions of the test method.
4.3 Occasionally certain used oils give no inflection in the forward titration mode, in which case a back titration modification with sodium acetate titrant is employed.
5. Significance and Use
5.1 New and used petroleum products can contain basic constituents that are present as additives. The relative amounts of these materials can be determined by titration with acids. The base number is a measure of the amount of basic substance in the oil, always under the conditions of the test. It is sometimes used as a measure of lubricant degradation in service; however, any condemning limits must be empirically established.
