Spectrophotometric determination of enrofloxacin and pefloxacin through ion-pair complex formation

Two simple, quick and sensitive spectrophotometric methods are described for the determination of enrofloxacin and Pefloxacin. The methods are based on the reaction of these drugs with bromophenol blue (BPB) and methyl orange (MO) in buffered aqueous solution at pH 2.3-2.5 in case of bromophenol blue and at pH 3.6 with MO to give highly coloured complex species, extractable with chloroform. The coloured products are quantitated spectrophotometrically at 420 and 424 nm for BPB and MO, respectively. Optimisation of the different experimental conditions is described. Beer's law is obeyed in the concentration ranges 2-12 and 2-18 microg ml(-1) with BPB and in the ranges 1-12 and 4-40 microg ml(-1)with MO for enrofloxacin and pefloxacin, respectively. The proposed methods are applied for determination of Enroxil oral solution, Peflacine tablets and Peflacine ampoules with mean percentage accuracies 99.5+/-0.99, 99.39+/-1.05 and 100.02+/-0.895, respectively, with BPB and 100.30+/-0.89, 100.25+/-0.98 and 100.20+/-0.72, respectively, with MO.