IP 417: Determination of base number - Potentiometric titration method

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  • Method adopted/last revised: 2004
  • Method reapproved: None
  • REF/ISBN: IP417-2938621
  • Status: Current
  • First printed in STM books: February 2013


This standard specifies procedures for determining the basic constituents in petroleum products and lubricating oils (see note 1). The method resolves these constituents into groups having weak-base, and strong-base ionization properties provided the dissociation constants of the more strongly basic compounds are at least 1000 times those of the next weaker groups.

NOTE 1 In new and used lubricating oils, the constituents that may be considered to have basic properties include organic and inorganic bases, amino compounds, salts of weak acids (soaps), basic salts of polyacidic bases, salts of heavy metals, and additives such as inhibitors and detergents.

The method may be used to indicate relative changes that occur in a lubricating oil during use under oxidizing conditions regardless of the colour or other properties of the resulting oil (see note 2). Although the titration is made under definite equilibrium conditions, the method is not intended to measure an absolute basic property that can be used to predict performance of a lubricating oil under service conditions. No general relationship between bearing corrosion and base number is known.

NOTE 2 The base number obtained by this standard may or may not be numerically the same as that obtained in accordance with IP 139.

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