Study on the resonance Rayleigh scattering, second-order scattering and frequency doubling scattering spectra of the interactions of palladium(II)–ceftriaxone chelate with anionic surfactants and their analytical applications

In pH 1.8–2.9 Britton–Robinson (BR) buffer medium, ceftriaxone (CTRX) can react with palladium(II) (Pd(II)) to form 1:2 cationic chelate, which can further react with anionic surfactants (AS) such as sodium lauryl sulfonate (SLS), sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) to form 1:3 ion-association complexes. As a result, the resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency doubling scattering (FDS) were enhanced greatly. The maximum RRS, SOS and FDS wavelengths of three ion-association complexes were located at 335 nm, 560 nm and 390 nm, respectively. The increments of scattering intensity (ΔI) were directly proportional to the concentrations of CTRX in certain ranges. The detection limits (3σ) of CTRX for SLS, SDBS and SDS systems were 1.8 ng ml−1, 2.3 ng ml−1 and 2.3 ng ml−1 (RRS method), 4.9 ng ml−1, 7.4 ng ml−1 and 4.7 ng ml−1 (SOS method) and 6.8 ng ml−1, 7.3 ng ml−1 and 9.1 ng ml−1 (FDS method), separately. The sensitivity of RRS method was higher than those of SOS and FDS methods. The optimum conditions of RRS method and the influence factors were investigated, and the composition of ion-association complexes and the reaction mechanism were discussed also. The effects of foreign substances were tested and it showed that the method has a good selectivity. Based on the ion-association reaction, the sensitive, simple and rapid methods for the determination of CTRX have been developed.