ANALYSIS OF COMPLEX SURFACTANT SYSTEMS - A CLASSICAL APPROACH

This paper describes an analytical method for quantitative estimation of soap, fatty acid non-ionics, anionics (other than soaps) and amphot erics when present as mixtures in liquid, gel, laundry and toilet soap s using classical analytical techniques. The methodology described ove rcomes the current problems associated with the analysis of mixed surf actants. Non-ionic surfactant and free fatty acids are separated from soap and amphoteric surfactant as acetone solubles. Part of the aceton e solubles is titrated with standard sodium hydroxide solution using p henolphtalein to determine free fatty acids Another part of acetone so luble is evaporated after neutralising the free fatty acid with alkali , the residue dissolved in water and extracted with ethyl acetate. The residue obtained from ethyl acetate evaporation is weighed as non-ion ic surfactant. From the acetone insoluble matter; soap along with amph oteric surfactant and some anionic surfactant (other than soap) is ext racted with rectified spirit or absolute alcohol. Rectified spirit ext ract is partially evaporated diluted with water to 50% v/v alcohol con tent (approximate), split with mineral acid and extracted with petrole um ether. The petroleum ether extract obtained is washed with sodium b icarbonate solution to remove anionic surfactant (other than soap) and amphoteric surfactant and evaporated. The TFM and anhydrous soap are estimated using the conventional methods [I]. Amphoteric surfactant is estimated gravimetrically from the aqueous/alcoholic solution obtaine d after fatty-acid extraction [2]. Anionic surfactant (other than soap ) is determined by two-phase titration with benzethonium chloride (Hya mine 1622) wing mixed indicator on a separate sample [3,4].