Complexation equilibria between antibacterial drugs and tungstate, molybdate and vanadate applied to their determination in pure and dosage forms

The complexation equilibria between norfloxacin (NOR), ciprofloxacin (CIP) and ofloxacin (OFL) with tungstate, molybdate and vanadate have been studie d by conductometric, potentiometric and spectrophotometric methods. The 1:1 ion association complex formed in solution and their stability constants w ere calculated by potentiometric and spectrophotometric methods at 25 +/- 2 degreesC. The complexes formed at the optimum conditions obeyed Beer's law within the range 0.2-12.0 mug mL(-1). The molar absorptivity and Sandell s ensitivity are also calculated, and the interference from the common additi ves or excipients has been studied. The results showed recovery of 99.7 +/- 0.9%, with relative standard deviations below 1.4%. The proposed method wa s successfully applied to the determination of the drugs in pharmaceutical formulations. A good precision and no significance difference with the resu lts obtained by the official methods are demonstrated via t-and F-values.