Abstract
A colloidal titration method for ionic surfactants with bromochlorophenol blue(BCPB) as an indicator was examined. A monovalent dye anion HBCPB- reacts with cations (C+) such as polydiallyldimethylammonium chloride (Cat-Floc) and quaternary ammonium salt containing a long-chain alkyl group, to form an ion associate (C+)2·BCPB2-, causing a color change from yellow to blue. An anionic surfactant (AS) solution at pH 3.3 is titrated with a polycationic titrant, Cat-Floc, until an ion association of AS with Cat-Floc, followed by the formation of a 2 : 1 ion associate (Cat-Floc+)2· BCPB2- causes a color change from yellow to blue. A cationic surfactant (CS) solution at pH 3.3 is titrated with a polyanionic titrant, polyvinylsulfate (PVSK), until CS forms a 1: 1 ion associate CS+·PVSK- rather than a 2:1 ion associate (CS+)2·BCPB2-to cause a color change from blue to yellow. AS at concentrations from 10-5 to 10-4 mol dm-3 and CS at concentrations from 10-5 to 4×10-4 mol dm -3 could be determined by the proposed method. The proposed method was applied to the determination of anionic surfactants in commercial detergents, and the results were in good agreement with those of the JIS titration method (Epton method).
