A Simple Rapid Method for Direct Determination of Total Fatty Matter in Soaps

Abstract

AbstractA rapid single step method for direct determination of total fatty matter (TFM) of soaps has been developed. The procedure involves two‐phase titration of a 2% solution of soap in ethanol : 2‐propanol (4 : 1 v/v) under alkaline conditions with 0.01 M solution of p‐tert. octyl phenoxyethoxy ethyl dimethyl benzyl ammonium chloride (Hyamine 1622) using bromocresol green as indicator. The method eliminates the tedious and time‐consuming ether extraction procedure and is applicable in the presence of all non‐fatty constituents normally present in soaps and also in the presence of unsaponified oil, if any, in the soap. The TFM of soaps with mean molecular weights varying from 200 to 300 can be determined with reasonable accuracy. The relative standard deviation for 0.04 to 0.11 millimole of TFM (mean molecular weight range 280–300) in soaps is in the range of 0.3–2.0. The method cuts down the time of TFM analysis from a minimum of 2 hours (for conventional ether extraction method) to less than 15 minutes from the time the material is available in solution. A special feature of the method is that it enables determination of alcohol‐insolubles as well as free alkali of the soap without necessitating any additional arrangement.