Study on the interactions of antiemetic drugs and 12-tungstophosphoric acid by absorption and resonance Rayleigh scattering spectra and their analytical applications.

In 0.1 mol L(-1) HCl medium, antiemetic drugs (ATM), such as granisetron hydrochloride (GS) and tropisetron hydrochloride (TS), reacted with H(3)PW(12)O(40)·nH(2)O and formed 3:1 ion-association complex of [(ATM)(3)PW(12)O(40)], then self-aggregated into nanoparticles-[(ATM)(3)PW(12)O(40)](n) with an average size of 100 nm. The reaction resulted in the enhancement of resonance Rayleigh scattering (RRS) and the absorption spectra. The increments of scattering intensity (ΔI(RRS)) and the change of absorbance (ΔA) were both directly proportional to the concentrations of ATM in certain ranges. Accordingly, two new RRS and spectrophotometric methods were proposed for ATM detection. The detection limits (3σ) of GS and TS were 3.2 ng mL(-1) and 4.0 ng mL(-1)(RRS method), 112.5 ng mL(-1) and 100.0 ng mL(-1)(spectrophotometric method). These two methods were applied to determine GS in orally disintegrating tablets and the results were in good agreement with the official method. The ground-state geometries and electronic structures of GS and TS were optimized by the hybrid density functional theory (DFT) method and the shape of [(ATM)(3)PW(12)O(40)](n) was characterized by atomic force microscopy (AFM). Take the RRS method with higher sensitivity as an example, the reaction mechanism and the reasons for enhancement of scattering were discussed.