Resonance Rayleigh scattering spectra of ion-association nanoparticles of [Co(4-[(5-chloro-2-pyridyl) azo]-1, 3-diaminobenzene)2]2+-sodium dodecyl benzene sulfonate system and its analytical application.

In pH 1.8-3.0 Britton-Robinson (BR) buffer solution, cobalt (II) reacts with 4-[(5-Chloro-2-pyridyl) azo]-1, 3-diaminobenzene (5-Cl-PADAB, L) to form a cationic chelate CoL(2). When interacting with anionic surfactants (AS) such as sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate (SDS) or sodium dodecyl sulfonate (SLS), the chelate can only react with SDBS to form ternary ion-association complexes ([CoL(2)]SDBS). By virtue of the extrusion action of water and Van der Waals force, the hydrophobic ion-association complexes draw close to each other and further aggregate to form {[CoL(2)]SDBS}(n) nanoparticles with an average diameter of 30 nm. As a result, resonance Rayleigh scattering (RRS) is enhanced greatly and new RRS spectra appear. Under the same conditions, both SDS and SLS exhibit no similar reactions and do not result in obvious change of RRS. Therefore, SDBS can be determined selectively by RRS method in the presence of SDS or SLS. The wavelength of 516 nm was chosen as a detection wavelength, the linear range and the detection limit (3sigma) are 0.05-6.0 microg mL(-1) and 0.015 microg mL(-1) for the determination of SDBS, respectively. The characteristics of RRS spectra of the CoL(2)-SDBS system, the optimum conditions of the reaction and the influencing factors have been investigated. The effects of coexisting substances have been examined too, indicating a good selectivity of the method for the determination of SDBS. The method can be used for the determination of SDBS in waste water and river water samples, and the results are satisfactory compared with those of standard samples of SDBS. Based on the formation of {[CoL(2)]SDBS}(n) nanoparticles, a sensitive, simple and rapid method has been developed for the determination of SDBS in environmental water samples using a RRS technique. Moreover, the reaction mechanism was discussed.