Spectrophotometric micro-determination of three quinolones antibacterial drugs in pure and in pharmaceutical dosage forms by reactions with diphenylamine sulphonate redox indicator

Abstract

In the present study, reliable, sensitive and efficient spectrophotometric methods for the determination of three quinolones, namely Ciprofloxacin (CP), Norfloxacin (NOR) and Nalidixic acid (NA) have been performed either in pure or in pharmaceutical dosage forms. The methods are based on the reaction of the studied drugs with diphenylamine sulphonate (DPAS) indicator in its oxidized form obtained by titration with potassium dichromate in sulfuric acid medium. For a first time, DPAS is used as an oxidant spectrophotometric self-indicator. It involved follow DPAS reactions with quinolones; where two reaction products are formed in two concentration ranges of each drug; and two mechanisms of reactions are involved. In the first reaction mechanism drugs reduce DPAS oxidant (violet form) and the concentrations are micro-determined by absorbance measurement at concentration ranges 11.6 – 92.9, 19.3– 154.3 and 15.9– 127.7 μgml^-1 and at λmax =545 -550 nm for NA, CIP and NOR respectively. In the second mechanism their concentrations are micro-determined via ion pair formation (brown form) after 30 min and measured at concentration ranges 2.3 – 9.3,1.9 – 15.4 and 1.6– 12.7 μgml^-1 and at λmax = 245, 280, and 285 nm for NA, CIP and NOR respectively. The results of two reaction mechanisms are compared and validated statistically by % recovery and SD values. The values of % recovery is found to be 99.98, 99.86, and 100.58 and those of SD are 0.33, 0.24, and 0.31in violet forms; while % recovery = 99.65, 99.7 and 99.95; SD = 0.011, 0.012 and 0.032in brown forms for CIP, NA and NOR respectively. The robustness and ruggedness of the results obtained by the second mechanism are checked by inter and intra-days results. The whole results obtained by the two mechanisms are also found to be in good agreement with those given by the official methods as confirmed by F- and t- tests.