FLUORESCENCE REACTION AND COMPLEXATION EQUILIBRIA BETWEEN NORFLOXACIN AND ALUMINUM(III) ION IN CHLORIDE MEDIUM

Norfloxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7- (1-piperazinyl)-3-quinoline carboxylic acid (NORH), reacts with aluminium(III) ion forming the strongly fluorescent complex [Al(HNOR)](3+), in slightly acidic medium. The complex shows maximum emission at 440 nm with excitation at 320 nm. The fluorescence intensity is enhanced upon addition of 0.5% sodium dodecylsulphate. Fluorescence properties of the Al-NOR complex were used for the direct determination of trace amounts of NOR in serum. The linear dependence of fluorescence intensity on NOR concentration, at a NOR to Al concentration ratio of 1:10, was found in the concentration range 0.001-2 mu g/ml NOR with a detection limit of 0.1 ng/ml. The ability of aluminium(III) ion to form complexes with NOR was investigated by titrations in 0.1 M LiCl medium, using a glass electrode, at 298 K, in the concentration range: 2 X 10(-4)less than or equal to[Al]less than or equal to 8 X 10(-4); 5 X 10(-4)less than or equal to[NOR]less than or equal to 9 X 10(-4) mol/dm(3); 2.8 less than or equal to pH less than or equal to 8.3. The experimental data were explained by the following complexes and their respective stability constants, log(beta+/-sigma): [Al(HNOR)], (14.60+/-0.05); [Al(NOR)], (8.83+/-0.08); [Al(OH)(3)(NOR)], (-14.9+/-0.1), as well as several pure hydrolytic complexes of Al3+. The structure of the [Al(HNOR)] complex is discussed, with respect to its fluorescence properties.