IP 149: Petroleum products - Lubricating oils and additives - Determination of phosphorus content - Quinoline phosphomolybdate method

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  • Method adopted/last revised: 1993
  • Method reapproved: 2003
  • REF/ISBN: IP149-2935231
  • Status: Current
  • First printed in STM books: January 1993


This international Standard specifies a quinoline phosphomolybdate method for the determination of the phosphorus content of unused lubricating oil and additive concentrates. The method is applicable to products containing any of the phosphorus compounds in normal use and having phosphorus contents between 0,005 and 10.0 % (m/m).

NOTE - There is no reason to doubt its applicability to filtered, used lubricating oils, but no systematic study of this application has been made.

The method is free from most interferences because the high insolubility of the quinoline phosphomolybdate precipitate leads to constant composition and freedom from most adsorbed or occluded impurities, especially from cations which would otherwise interfere in the subsequent titration of the precipitate.

NOTE - Barium, calcium, magnesium, zinc, iron, aluminium, alkali salts, citric acid and citrates, chromium up to 18 times the phosphorus content and titanium up to 3.5 times do not interfere with the method.

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