Rapid and simple determination of a cationic surfactant by adsorption induced by vigorous shaking

A rapid and simple method for the determination of a cationic surfactant is described. The method is based on the formation of an ion associate with tetraphenylporphinetetrasulfonic acid (TPPS) and zephiramine as an example of a cationic surfactant. The ion associate was adsorbed on the inner wall of the vessel by vigorous shaking. After complete removal of the solution in the tube, the ion associate was dissolved with 50% ethanol and measured spectrophotometrically. The proposed method is simple and rapid. The apparent molar absorption coefficient for zephiramine using 20 mL of sample and 5 mL of eluent was estimated to be 9.01 x 10(4) L mol(-1) cm(-1) at 415 nm. The coefficient of variation for 20.2 mug of zephiramine was 5.9% (n=10).