Eosin Y (EY), a dye, can emit strong fluorescence, while propafenone (PPF) is also a fluorescent species. The wavelength of maximum emission of them in solution of pH 2.5～3.8 is at 549 nm (EY) and 419 nm (PPF), respectively. Their respective spectra are far from each other so that they can be separated. The fluorescence quenching of both EY and PPF could be observed when they reacted to form complexes, which indicated that this was a mutual fluorescence quenching system. When EY was used as a probe for the determination of PPF, the detection limit (3σ) was 9.4 ng/mL|contrariwise, when PPF was used as a probe, the detection limit for EY (3σ) was 259.7 ng/mL. The former had higher sensitivity so that it was more suitable for the determination of trace PPF. The optimum reaction conditions, influencing factors and analytical properties had been studied. In addition, the discussion on the reaction mechanism, composition and structure of the complex suggests that EY reacted with PPF to form a 1∶1 complex via electrostatic forces, hydrophobic interaction, aromatic stacking interaction and hydrogen bonding. Meanwhile, this fluorescence quenching was a static quenching process. The method was satisfactorily applied to the determination of PPF in tablets and human serum.

Key words: propafenone, eosin Y, mutual fluorescence quenching