IP 400: Determination of base number of petroleum products - Conductimetric titration method

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  • Method adopted/last revised: 2001
  • Method reapproved: None
  • REF/ISBN: IP400-2935507
  • Status: Current
  • First printed in STM books: January 2001


This standard specifies a conductimetric titration method for the determination of the base number (BN) of petroleum products. It is suitable for both new and used products having base numbers from 1 mg to 40 mg KOH/g.

NOTE 1 - The method detects the relative changes that occur in the BN of an oil during use in an engine but any condemning limits have to be empirically established. Although the analysis is made under closely specified conditions, the method is not intended to, and does not report basic properties which can be used to predict the performance of an oil.

NOTE 2 - This method may be used for petroleum products having base numbers greater than 20 mg KOH/g, lubricant additives and additive packages but it will be necessary to dilute the sample in order to obtain a suitable sample weight. This will give an approximate base number because whilst this method is capable of measuring the basic constituents of these products the precision has been validated only in the range 1 to 20 mg KOH/g.

NOTE 3 - The base number expressed in mg KOH/g is a guide in the quality control of lubricating oil formulations and this method may be used for other petroleum products including lubricant additives and additive packages. The method may also be used as a measure of lubricant degradation in service as part of a used oil analysis programme.

NOTE 4 - Fully automated conductimetric titration systems may be used provided they have been proven, by use of an internal standard of known base number, to give a result equivalent to that obtained by the referee manual titration method. Some may require a fixed volume of sample to be used, which may necessitate dilution of the sample prior to injection if a high base number is expected. They should record the complete course of a titration by continuously printing out the conductivity or change in conductance versus the volume of titrant added.

NOTE 5 - For the purposes of this standard, the terms "% (m/m)" and "% (V/V)" are used to represent respectively the mass fraction and the volume fraction.

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