ASTM D94 standard test method for saponification number of petroleum products
4. Summary of Test Method
4.1 A known mass of the sample is dissolved in a suitable solvent, such as butanone (methylethylketone), xylenes, or Stoddard Solvent, or a combination thereof (Warning - Extremely flammable. Vapors can cause flash fire), and is heated with a known amount of alcoholic potassium hydroxide (KOH). The excess alkali is titrated with standard acid, and the saponification number is calculated.
4.2 The titration end point can be detected either colorimetrically (Method A) or potentiometrically (Method B).
5. Significance and Use
5.1 Petroleum products can contain additives that react with alkali to form metal soaps. Fats are examples of such additives. Also, certain used engine oils, especially from turbine or internal combustion engines, can contain chemicals that will similarly react with alkali. The saponification number expresses the amount of base that will react with 1 g of sample when heated in a specific manner. This then gives an estimation of the amount of acid present in the sample, that is, any free acid originally present plus any combined (for example, in esters) that have been converted to metal soaps during the heating procedure.
5.2 Saponification numbers are also used in setting product specifications for lubricants and additives.
