Resonance Rayleigh scattering spectra of the interaction of Pd(II)-methotrexate chelate with methylene blue and their analytical application

In Britton-Robinson buffer of pH 4.1-7.0, methotrexate reacts with palladium(II) to form 1:1 anionic chelates. Which react further with methylene blue (MB) to form the ion-association complexes. In this case, the resonance Rayleigh scattering (RRS) intensities are enhanced greatly and new RRS spectra appear. The maximum RRS wavelengths locate at 342 nm. Under given conditions the intensities of RRS are proportional to the concentration of MTX. The linear range is 0.008-2.0μg/mL for the system, and the methods have high sensitivities and the detection limits of MTX is 2 ng/mL. The optimum conditions of the reaction, influence factors and the effect of coexisting substances were investigated. A high sensitive, simple and quick method is developed for the determination of MTX. The method can be applied satisfactorily to determination of MTX in serum and urine samples. In addition, the structure of the ternary ion-association complex and their reaction mechanism were discussed.