Colorimetric determination of the fluoroquinolones.

Ciprofloxacin, ofloxacin and norfloxacin formed an amber coloured complex with iron(III) nitrate nonahydrate. The complex, which formed instantaneously at room temperature, was stable. The solutions of the complex obeyed Beer's law at 370 nm, the wavelength of maximum absorption of radiation (lambda[max]). The A(1%) for norfloxacin, ofloxacin and ciprofloxacin was 202, 207 and 235 respectively. The formation of the complex was the basis for the quantitative and qualitative determination of the drugs. There was statistically no significant difference (P < 0.05) between the results obtained quantitatively by this colorimetric method and those obtained by the microbiological assay method.