Fading Spectrophotometric Method for Determination of Cationic Surfactants with Eosin Y and Ethyl Eosin

In HCl-NaOAc buffer medium,cationic surfactants(CS) reacts with eosin Y(EY) or ethyl eosin(EE) to form an ion-association complex,the colors of solutions fade obviously,the maximum fading wavelength at 514 nm and 516 nm,besides,there is an absorption peak at 548 nm and 544 nm.The fading intensity is also proportional to the concentration of cationic surfactants at the maximum fading wavelength,a sensitive spectrophotometric method is developed for determination of cationic surfactants.The concentration of CS in the range of 0～4.79×10-5 mol/L obeys Beer' law at the maximum fading wavelength,the apparent molar absorptivity are from 2.75×104 L/(mol·cm) to 3.41×104 L/(mol·cm),the detection limit are from 7.87×10-7 mol/L to 8.97×10-7 mol/L.The method has high sensitivity and fairly good selectivity,the method is applied to the determination of CS in water samples,with satisfactory results.