OELCHECK test instrument: Metrohm 855 Robotic Titrosampler, Mettler titrator DL 53 with sample changer Rondo 60
Sample volume: 5 ml
Unit: mgKOH/g
Test result: BN (Base Number)
Result range: 0.5 - 99 mg KOH/g
Analysis for: Engine oils and some refrigerator oils
Brief description: The BN is determined by titration. In that process, a titrant (perchloric acid) is added to an oil-solvent mixture until it is “neutral“. This is detected potentiometric and shown by an inflection point in the titration curve. Using titrant up to this inflection point, the BN can be calculated in mgKOH/g.
Statement: The BN states the alkaline reserve of a lubricant for the neutralisation of acids which may be produced during a combustion process, for instance. The change in BN compared to fresh oil gives a key indication regarding continued use of the oil.
Underlying test standards: DIN 51639-1
Deviating methods: ASTM D4739: Using a different titrant (HCI)
Comparable methods:

ISO 3771: Determination of the BN - Potentiometric titration with perchloric acid

ASTM D2896: Determination of the BN of petroleum products by potentiometric perchloric acid titration