Determination of long chain quaternary ammonium salts in the mixtures of cationic and nonionic surfactants was attempted. The quaternary ammonium salt reacted with potassium dichromate in an aqueous solution to give a precipitate composed of 2 mole quaternary ammonium and 1 mole dichromate ion. The precipitate, separated by filteration, was dissolved in methanol and the absorbance of the methanol solution was measured at 355mμ.
Sufficient results were obtained for the determination of all used cationic surfactants-lauryl-, cetyl-, stearyl-trimethylammonium chlorides, myristyl-, cetyl-benzyldimethylammonium chlorides, lauryl-, and cetyl-pyridinium chlorides.
The cationic surfactants could be determined in the presence of a large amount of polyethylene glycols (molecular weights (6008000)). The determination was not disturbed by the additions of non-ionic surfactants and inorganic salts until ten times as large in quantity as the cationic surfactant.