The interaction between palladium(II)-famotidine and halogen-fluorescein dyes (HF) was investigated by fluorescence and absorption spectrum. In pH 3.2～4.1 NaOAc-HOAc buffer medium, famotidine (FMTD) reacted with palladium(II) to form chelate cation, which further reacted with dibromofluorescein (DBF), eosine (EY), eosin (EE) and tetrabromotetrachloroflurescein (TCBF) to form ternary ion-association complexes [Pd(FMTD)]•(HF)₂. As a result, the absorption bands of DBF, EY, EE, TCBF were shifted and the fluorescences of them were quenched. The maximum absorption wavelengths of [Pd(FMTD)]•(HF)₂ were located at 541 (DBF system), 547 (EY system), 549 (EE system), 558 (TCBF system) nm and the maximum fluorescence emission wavelengths of them were located at 513～540 nm, the order of quenching values (ΔF) was DBF＞EY＞EE＞TCBF. The ΔF was proportional to the FMTD concentration in a certain range and the detection limit was 13.6～29.6 ng•mL^－1. Based on it, a high sensitive, good selective, simple, rapid and new fluorescence quenching method had been proposed to determine FMTD. It can be applied to determine FMTD in human urine after taking the medicine, which provide reference for pharmacokinetics of the FMTD. The composition and structure of [Pd(FMTD)]•(HF)₂ and fluorescence quenching mechanism were fully discussed.

Key words: fluorescence spectrum, famotidine, palladium(II), halogen-fluorescein