Under the simulated physiological conditions (at pH 7.40 and ionic strength＝0.15 mol/L), the intrinsic fluorescence of bovine serum albumin (BSA) was quenched by torasemide (TOR). From the change of absorption spectrum, the effect of temperature and the quenching constant, this procedure was judged to be static quenching process on account of the TOR interacting with BSA to form ground state coordination compounds. In this paper, the binding constants (K), the binding sites (n) and the thermodynamic properties between TOR and BSA had been calculated. The results show that the TOR can quench the fluorescence of BSA and the mechanism is static quenching process. The fluorescence of BSA was quenched regularly by the TOR in certain ranges. And at the maximum quenching wavelength 342 nm, the value of the fluorescence quenching (ΔF) was directly proportional to the concentration of TOR in the range of 0.02～5.0 mg/mL with the detection limit being 6.3 ng/mL. In the work, the optimum conditions and the influencing factors were investigated. The results showed that this method exhibited a high sensitivity and selectivity. Based on this, a novel fluorescence quenching method for the determination of trace TOR with BSA as a fluorescence probe has been developed. It has been applied to the determination of TOR urine samples after the patient having TOR and in tablets with satisfactory results.

Key words: torasemide, bovine serum albumin, fluorescence spectroscopy