Study on the resonance nonlinear scattering spectra of the interactions of promethazine hydrochloride and chlorpromazine hydrochloride with 12-tungstophosphoric acid and their analytical applications

In pH 1.0 HCl medium, 12-tungstophosphoric acid (TP) reacted with promethazine hydrochloride (PMZ) and chlorpromazine hydrochloride (CPZ) to form ion-association complexes, which led to a great enhancement of the resonance nonlinear scattering such as second-order scattering (SOS) and frequency doubling scattering (FDS). Their maximum SOS and FDS peaks were located at 585 nm (TP-PMZ), 584 nm (TP-CPZ) and 388 nm (TP-PMZ), 329 nm (TP-CPZ), respectively. These results provided some indication for the determination of PMZ and CPZ by SOS and FDS methods. The linear range of TP-PMZ and TP-CPZ systems were 0.0069-2.5 μg mL−1, 0.102-5.0 μg mL−1 (SOS) and 0.079-6.0 μg mL−1, 0.0133-5.0 μg mL−1 (FDS), respectively. The detection limits (3σ) of PMZ and CPZ were 2.08 ng mL−1, 3.07 ng mL−1 (SOS) and 2.22 ng mL−1, 3.98 ng mL−1 (FDS), respectively. In this work, the optimum reaction conditions, the influences of coexisting substances and ionic strength and analytical application have been investigated. The methods have been successfully applied to the determination of PMZ and CPZ in tablets. In addition, the composition of ion-association complexes and the reaction mechanism are also discussed.