Simple spectrophotometric determination of nonionic surfactants with a cationic azo dye

A simple spectrophotometric method for the determination of polyoxyethylene nonionic surfactants, such as TritonX-100 with 1-(p-phenylphenacyl)-4-(4-aminonaphthylazo)-pyridinium bromide(PPAP), was developed. PPAP was synthesized by quarternizing 4-(4-aminonaphthylazo)pyridine with p-phenylphenacyl bromide. Because PPAP was easily associated with nonionic surfactants to produce a blue ion associate in aqueous solution, the concentration of nonionic suifactants were determined by measuring the absorbance of ion associates at 612 nm. The apparent molar absorptivity of the TritonX-100 ion associate was 1.0 x 10(3) dm(3) mol(-1) cm(-1) at 612 nm. The calibration graph for TritonX-100 was linear over the range from 6.0 x 10(-5) to 8.0 x 10(-4) M, and the relative standard deviation for 5.6 x 10(-4) M of TritonX-100 was 2.0%. The proposed method was applied to the determination of nonionic surfactants in commercial domestic detergents.