Colourimetric and atomic absorption spectrometric determination of some f luoroquinolone derivatives

Three simple, accurate, sensitive and selective procedures for the determination of ten fluoroquinolones (amifloxacin, ciprofloxacin hydrochloride, difloxacin hydrochloride, enoxacin, enrofloxacin, lomefloxacin hydrochloride, lovefloxacin, norfloxacin, ofloxacin and pefloxacin mesylate) were described. Procedures I and II are based on the formation of ion-pair complexes between the drugs and ammonium reineckate reagent in an acidic medium at 25 ±2°C and the formed precipitates are quantitatively determined either colourimetrically (procedure I) or by atomic absorption spectrometrically (procedure II). Procedure I is based on dissolving the formed precipitate with acetone, the volume was completed quantitatively and the absorbance of the solution was measured at 527 nm against pure solvent blank. The formed precipitates on the atomic absorption spectrometric procedure (procedure II) are quantitatively determined either directly or indirectly through the chromium precipitate formed or the residual un-reacted chromium in the filtrate at 358.6 nm and the optimum conditions for precipitation have been carefully studied. Procedure Ill is based on the reaction of the studied drugs with 2,2-diphenyl-1-picrylhydrazyl reagent (DPPH). The latter is employed to abstract a hydrogen atom from the drugs thereby promoting a process of radical coupling. This results in a reduction of the violet color of DPPH with the formation of the yellow colored 2,2-diphenyl-1-picrylhydrazine (DPPH₂). The decrease in the intensity of the violet color is used to measure the concentration of the drugs. All measurements are made at λ = 520 nm on methanolic solutions of the reagent and drugs. Beer's law is obeyed for the studied drugs in the range 2-36 µg ml⁻¹ with correlation coefficients not less than 0.9992. All procedures hold well accuracy and precision when applied to the analysis of the cited fluoroquinolones in different dosage forms with good recovery percent ranged from 98.88±0.40 to 100.99±0.44 without interference from additives.