Resonance Rayleigh scattering for the determination of cationic surfactants with Eosin Y

Resonance Rayleigh scattering (RRS) of cationic surfactants-Eosin Y systems and their analytical application have been studied. In aqueous solution at pH 2 similar to 3, Eosin Y reacts with a monomer of cationic surfactants (CS), such as Zephiramine (Zeph), tetradecylpyridinium bromide (TPB), cetylpyridinium bromide (CPB), cetylpyridinium chloride (CPC) and cetyltrimethylammonium bromide (CTMAB), to form an ion associate and a new RRS spectrum appears. The spectral characteristics of the five ion associates are similar and their maximum scattering wavelengths (lambda(max)) are all at 313 nm. The intensity of RRS at lambda(max) of the ion associate is directly proportional to the concentration of CS in the range of 0-3.0 mu g/25 mL. The technique has high sensitivity for the determination of CS; their detection limit is between 5.57 ng/mL and 7.60 ng/mL depending on the CS. In this case, most metal and non-metal ions, NH4+ and some anionic surfactants do not interfere, so that the method has a good selectivity. It can be applied to the determination of trace amounts of cationic surfactants in water samples.