Stability-indicating methods for the spectrophotometric determination of norfloxacin

Two spectrophotometric procedures for the selective determination of norfloxacin (NF) in the presence of its decarboxylated degradant are described. The first depends upon measurement of the pH-induced absorbance difference (delta A) of the drug solution between 0.1 N HCl and 0.1 N NaOH at 280 nm. The second involves chelation of the intact drug with iron (II) in acetate buffer solution (pH 5.7 +/- 0.1) to form a yellow-coloured chelate which absorbs at 358 nm. The two procedures are applied successfully for the determination of the intact drug both in pure form and in tablet form. The two methods retain their accuracy in the presence of up to 62% and 76% degradants, respectively.