OELCHECK test instrument: Metrohm 855 Robotic Titrosampler, Mettler Toledo Excellence titrator 90
Sample quantity: 5 ml for AN
Unit: mgKOH/g
Test result: AN (Acid Number), SAN (Strong Acid Number)
Result range: 0,1 - 150 mg KOH/g
Analysis for: all industry oils e.g. from gears, hydraulics, oil circulation systems, transformer oils, heat transfer systems, landfill gas engines
Brief description: The AN indicates the amount of potassium hydroxide required to neutralise the acids contained in a gram of oil. If the sample is too dark to determine the neutralisation number at which an indicator, when added to a mixture of oil and solvent, will indicate the neutral state through a colour change, the AN shall be determined for these samples. In that instance, a titrant (KOH) is added to the mixture of oil and solvent until the mixture is "neutral". This is detected using a potentiometer and is shown by an inflection point in the titration curve. Using titrant up to this inflection point indicates the AN.
Statement: By comparison with the fresh oil values, the AN allows conclusions to be drawn regarding the oxidation of the oil and the breakdown of oil additives. It provides essential supplementary information for the extension of oil change intervals. The SAN (Strong Acid Number), unit mgKOH/g, is only recorded in AN titration when the oil contains strong, aggressive acids, such as those used in gas engines with landfill gas.
Underlying test standard: ASTM D664
Deviating methods: DIN EN 12634: another solvent and titrant used and SAN not recorded
Comparable methods: DIN ISO 6618: neutralisation number determined using a photometer