Spectrofluorimetric, Atomic Absorption Spectrometric and Spectrophotometric Determination of Some Fluoroquinolones

Simple, accurate, sensitive and selective spectrofluorimetric, atomic absorption spectrometric and spectrophotometric methods are described for the quantitative determination of ten fluoroquinolones (amifloxacin, ciprofloxacin hydrochloride, difloxacin hydrochloride, enoxacin, enrofloxacin, lomefloxacin hydrochloride, levofloxacin, norfloxacin, ofloxacin and pefloxacin mesylate). The first method was a spectrofluorimetric method in which samples of the studied drugs in 0.1 N H₂SO₄ showed native fluorescence at 450 nm when excitation was at 290 nm. The calibration graph was rectilinear from 0.3-1.4 μg mL^-1 (method I). Cobalt sulphate was used for precipitation of the ion associates formed from the reaction with the cited drugs. The formation and solubility of the solid complexes at the optimum conditions of pH and ionic strength values have been studied. The method depends on direct determination of the ions in the precipitate or indirect determination of the ions in the filtrate by atomic absorption spectroscopy. The optimum conditions for precipitation were carefully studied. Rectilinear calibration graphs were obtained in the range of 3-30 μg mL^-1 for each of the investigated drugs. The molar ratios of the formed chelats were determined by Job's method and their association constants were also calculated (method II). Ammonium vanadate was used for the spectrophotometric determination of the selected fluoroquinolones by oxidation in sulphuric acid medium resulting in the development of a greenish blue colour measured at 766 nm which was attributed to the vanadium (IV) produced by reduction of vanadium (V) by the selected drugs. The optimum conditions for heating time, reagent concentration and sulphuric acid concentration were carefully studied. The accuracy and precision of the proposed method was confirmed by estimating five or six replicates within Beer's law limits were obtained in the range 10-40 μg mL^-1 for each of the investigated drugs with correlation coefficients not less than 0.9994 for the investigated drugs (method III). The developed spectrofluorimetric, atomic absorption spectrometric and spectrophotometric methods were applied successfully for the determination of the studied drugs in their pharmaceutical dosage forms with a good precision and accuracy compared to official and reported methods as revealed by t-and F-tests. The first method was approximately ten times more sensitive than the second and third methods. Atomic absorption spectrometric method was also applied for the determination of studied drugs in spiked urine and plasma samples.