Analysis of zinc dialkyl dithiophosphates by nonaqueous capillary electrophoresis and application to lubricants

Capillary electrophoresis has been successfully applied to the separation of four different commercial zinc dialkyldithiophosphate (ZDDP) mixtures and to the analysis of the ZDDP in fresh and used lubricating oil. Nonaqueous systems composed. of methanol, tetrahydrofuran, and acetonitrile with tetraethylammonium, tetramethylammonium, or ammonium hydroxide and acetic acid as buffer additives were employed to separate the metal complexes according to the different hydrocarbon chain lengths and structures of the alkyl substituents. (C) 1999 John Wiley & Sons, Inc.