Abstract: In an acid solution, an isopoly-acid anion such as isopoly-molybdic acid or isopoly-tungstic acid could react with prazosin hydrochloride(PRH) and doxazosin mesyllate(Dox)α1-receptor blocker drugs to form ion-association complexes respectively. It resulted in the great enhancement of resonance Rayleigh scattering(RRS) intensities and new RRS peaks. The maximum RRS wavelength was located at 367 nm for isopoly-molybdic acid system and 290 nm for isopoly-tungstic acid system. The reaction products of the two drugs had similar spectral characteristics. The optimum pH ranges were 2.1～2.3 for isopolymolybdic acid-PRH system and 3.1～3.3 for isopoly-tungstic acid-PRH system. In a certain range, the intensities of RRS were directly proportional to the concentration of drugs for the two different reaction systems. The reactions exhibited a high sensitivity, with a detection limit (3σ/s) of 4.76 μg/L(isopoly-molybdic acid-PRH system) and 9.88 μg/L(isopoly-tungstic acid-PRH system) for PRH, and also showed a good selectivity. The method was applied to the determination of α1-receptor blocker drugs in tablets and human urine samples. Density functional theory(DFT) calculations with Gaussian 03W at B3LYP/6-31G level were performed to calculate the charge distribution of PRH for investigating the reaction mechanism; in addition, the reasons for the RRS enhancement of the system were discussed.

Key words: prazosin hydrochloride, doxazosin mesyllate, Resonance Rayleigh Scattering, molybdate, tungstate