In pH 1.8～3.0 BR buffer medium, Co(II) was reacted with 2-(5-bromo-2-pyridylaro)-5-diethylaminophenol (5-Br-PADAP)(HL) to form a cationic chelate Co[(HL)2]2＋. In this case, only the characteristics of the absorption spectra were changed, but the intensities of the resonance Rayleigh scattering (RRS) did not increase. When the cationic chelate was further reacted with some anionic surfactants such as sodium dodecylbenzenesulfonate (SDBS), sodium dodecyl sulfate (SDS) and sodium laurylsulfonate (SLS), only SDBS formed a ternary ion-association complex resulting in the great enhancement of the RRS. The RRS peaks for the ion-association complex are located at 306, 370 and 650 nm, respectively. There was a linear relationship between the RRS intensity (ΔI) and the SDBS concentration in a certain range. The detection limit was 0.043 mg•mL－1 and the linear range was 0.14～6.0 mg• mL－1 at 650 nm. In this work, the characteristics of the RRS spectra, the optimum conditions of the reaction and the properties of analytical chemistry were investigated. A new method for the selective determination of SDBS in the presence of some other anionic surfactants such as SDS and SLS has been developed, which is sensitive, simple and fast. It can be applied to the determination of SDBS in natural water and waste water samples with satisfactory results. In addition, the reaction mechanism was also discussed.

Key words: resonance Rayleigh scattering, Co(Ⅱ), 5-Br-PADAP, sodium dodecylbenzenesulfonate