ASTM D4739 Base Number Determination by Potentiometric Hydrochloric Acid Titration
Some additives in lubricating oils are basic, and absorb acids that form due to oxidation. The level of basic components is indicated by base number – a high base number indicates a high level of basic components, a low number indicates a low level. This test determines base number. In service oils it may predict the oil's ability to absorb acids as they are produced; changes in base number may indicate additive depletion.
The sample is accurately weighed into the titration vessel, solvent is added and the electrodes are immersed. The sample is titrated with alcoholic potassium hydroxide, and meter readings recorded, plotted and the endpoint is determined. The base number is reported in mg KOH per gram of sample.
Related test offered by Petro-Lubricant Testing Laboratories:
For new oils or for oils where both strong and weak bases are of interest:
ASTM D2896 Base Number in Petroleum Products by Potentiometric Perchloric Acid Titration
For base number determination colorimetrically:
ASTM D974 Acid and Base Number by Color-Indicator Titration
Sample size: 20 g
- ASTM D974 – Acid and Base Number by Color-Indicator Titratiion; Neutralization Number
- ASTM D1093 – Acidity of Water Layer and distillation residues
- ASTM D1121 – Reserve Alkalinity of Antifreeze
- ASTM D2074 – Amine Value
- ASTM D2896 – Base Number – Perchloric Acid Method
- ASTM D2989 – Acidity-Alkalinity of Halogenated Solvents/Mixtures