The effect of surfactants on the pH transition interval of bromothymol blue immobilized on XAD 4

Abstract

Cationic, anionic and non-ionic surfactants adsorb readily from aqueous solution on to Amberlite XAD 4. The ionic surfactants cause the pH of the solution in contact with the resin to differ from that in the bulk of solution, cationic surfactants increasing the interfacial pH and anionic surfactants decreasing it. This causes a shift in the pH transition interval of a co-adsorbed pH indicator when measured with respect to the bulk solution. The quantity of ionic surfactant adsorbed tends to a constant value (presumably monolayer coverage) with increasing solution concentration, this amount being a function of the individual surfactant, whereas non-ionic surfactants readily form multilayers. Significant adsorption occurs when the surfactant possesses at least 14 carbon atoms.