Study on the interaction between palladium(II)-chlorpromazine hydrochloride and sodium tungstate by the resonance Rayleigh scattering, second-order scattering and frequency doubling scattering spectra and its analytical application

The interaction between palladium(II)-chlorpromazine hydrochloride and sodium tungstate was investigated by ultraviolet-visible absorption, resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency doubling scattering (FDS) spectroscopy. In pH 5.3 Britton-Robinson (BR) buffer medium, chlorpromazine hydrochloride (CPZ) reacted with Pd(II) to form 2:1 cationic chelate, which further reacted with Na2WO4 to form a 1:1 ternary ion-association complex ([Pd(CPZ)2]·WO4). As a result, the signal intensities of RRS, SOS and FDS were enhanced greatly, and the enhancements of scattering were proportional to the CPZ concentration in a certain range. Their maximum wavelengths were located at 310 nm, 570 nm and 391 nm, respectively and the detection limits (3σ) were 1.6 ng/mL (RRS method), 3.2 ng/mL (SOS method) and 5.6 ng/mL (FDS method). The optimum reaction conditions, the influences of coexisting substances and analytical application were mainly investigated by RRS method due to its highest sensitivity. A highly sensitive, simple, rapid and new method had been proposed to determine CPZ in the pharmaceutical form and residue of CPZ in pork. In addition, the Gibbs free energy change (δGf) of ion-association reaction was computed by using B3LYP/3-21g*/LanL2dz method. The formation of ion-association and the reasons for the enhancement of RRS were also discussed.