Abstract: In alkaline medium of pH=9.0, Hg2+ reacts with phenanthroline(phen) to form a colorless chelate [Hg(phen)3]2+, which further reacts with Congo red(CR) to form 1∶1 ion-association complex. As a result, new peaks appear in the spectra of resonance Rayleigh scattering(RRS), second order scattering(SOS) and frequency doubling scattering(FDS), and their intensities are enhanced greatly. The maximum peaks of RRS, SOS and FDS are located at 378 nm, 612 nm and 352 nm, respectively. The enhanced RRS, SOS and FDS intensities are directly proportional to the concentrations of Hg2+. These methods have very high sensitivities and good selectivities, and the detection limits are 2.32 μg/L for RRS, 3.20 μg/L for SOS, 1.56 μg/L for FDS, respectively. In addition, the influencing factors and the effects of coexisting substances of the reaction were examined by RRS under optimum conditions. The results show that this method has a good selectivity. Therefore, a new method has been developed to determine trace amounts of Hg2+. The reasons for RRS enhancement of the system and reaction mechanism have been investigated.

Key words: resonance rayleigh-scattering, Second-Order scattering (SOS), frequence doubling scattering, Mercury(Ⅱ), phenanthroline, Congo red