FLUOROQUINOLONES AS SENSITIZERS OF LANTHANIDE FLUORESCENCE - APPLICATION TO THE LIQUID-CHROMATOGRAPHIC DETERMINATION OF CIPROFLOXACIN USING TERBIUM

A time-resolved luminescence detection procedure is proposed for the in vivo liquid chromatographic determination of the important fluoroquinolone antibiotic ciprofloxacin. In a first step, the sensitized luminescence of lanthanides (samarium, terbium or europium) by three main fluoroquinolones, i.e. ciprofloxacin, pefloxacin and ofloxacin, was investigated. For this purpose, a preliminary study was made in order to determine the photophysical characteristics of the compounds of interest. Then, in the presence of lanthanide ions, the possibility of chelation, suggested by the alpha-keto acid skeleton of the fluoquinolone nucleus, was verified. Among the three lanthanides studied, Tb3+ was the most efficiently sensitized. Among the fluoroquinolones tested, ciprofloxacin was the best sensitizer. In a second step, the formation of a terbium chelate with ciprofloxacin was demonstrated in a classical reversed-phase eluent [methanol-water (50 + 50) containing trichloroacetic acid (pH 2.5)] using a postcolumn device. In this way, the ciprofloxacin-terbium chelate was selectivity excited at 320 nm and the terbium emission detected at 545 nm (D-5(4) --> F-7(5) main terbium transition). Postcolumn sensitization was performed using an alkaline methanolic reagent (1 X 10(-3) M Tb3+-2 X 10(-2) M triethylamine-1 x 10(-4) M trioctylphosphine oxide). The chemical compatibility between the eluent and the postcolumn reagent was studied. The analytical characteristics were established. With the proposed liquid chromatographic method, the time-resolved luminescence detection mode allowed the detection of 0.25 pmol injected of ciprofloxacin, which easily meets the sensitivity required for the determination of fluoroquinolones in biological samples.