Spectrophotometric determination of some fluoroquinolone antibacterials through charge-transfer and ion-pair complexation reactions

Two simple, rapid and sensitive spectrophotometric methods for the determination of three fluoroquinolones, namely levofloxacin, norfloxacin and ciprofloxacin have been performed either in pure form or in their tablets. In the first method, levofloxacin and norfloxacin are directly treated with bromocresol green (BCG) in dichloromethane while ciprofloxacin is allowed to react with the same dye in aqueous acidic buffer. Highly yellow colored complex species were formed instantaneously in case of levofloxacin and norfloxacin or after extraction into dichloromethane for ciprofloxacin. The formed complexes are quantified spectrophotometrically at their absorption maxima at 411 nm for levolloxacin and 412 nm for norfloxacin and ciprofloxacin. The second method involves the reaction of levofloxacin with rho-chloranilic acid (rho-CA) and norfloxacin with tetracyanoethylene (TCNE) in acetonitrile to give complexes with maximum absorbance at 521 and 333 nm for the two drugs, respectively. Adopting the first procedure, calibration graphs were linear over the range 1-20 mug mL(-1) with mean percentage recoveries of 100.41 +/- 0.72, 99.99 +/- 0.54 and 100.23 +/- 0.91 for the theree drugs, respectively. For the second procedure, the concentration ranges were 15-250 mug ml(-1) for levofloxacin using rho-CA and 0.8-16 mug mL(-1) for norfloxacin using TCNE with mean percentage recoveries of 99.88 +/- 0.45 and 100.26 +/- 0.68 for the two drugs, respectively. The proposed methods were successfully applied to determine these drugs in their tablet formulations and the results compared favorably to that of reference methods. The proposed methods are recommended for quality control and routine analysis.