SEQUENTIAL INJECTION TECHNIQUE EMPLOYED FOR STOICHIOMETRIC STUDIES, OPTIMIZATION AND QUANTITATIVE-DETERMINATION OF SOME FLUOROQUINOLONE ANTIBIOTICS COMPLEXED WITH IRON(III) IN SULFURIC-ACID MEDIA

A sequential injection spectrophotometric method for stoichiometric st udies, optimization and quantitative determination of ciprofloxacin an d norfloxacin was developed. The work is based on the complexation rea ction of ciprofloxacin and norfloxacin with iron(III) in sulfuric acid media and a spectrophotometric measurement of absorbances of the corr esponding complexes at 447 and 430 nm respectively. The stoichiometrie s and formation constants were determined. A 1:2 iron(III) to drug mol e ratio was found to give the most predominant complexes for both drug s with 5.00 x 10(-3) M H2SO4 and at 0.20 M ionic strength utilizing Jo b's method and the molar ratio method. A numerical method was utilized for the calculation of the formation constants, the logarithms of whi ch were found to be 7.756 +/- 0.121 and 7.839 +/- 0.056, for ciproflox acin and norfloxacin respectively. A factorial design together with th e all-model-search method was utilized for the optimization of the con centration and aspiration volume of iron(III) as these were the variab les which most affected peak absorbance. Working dynamic ranges of 50- 500 ppm and 50-400 ppm were obtained for ciprofloxacin and norfloxacin respectively. The method was found to be suitable for the determinati on of these compounds in pharmaceutical preparations.