Three simple and accurate spectrophotometric methods have been developed for the selective determination of enrofloxacin )EN) and flumequine (FL) in presence of their decarboxy1ated degradates. The first method is based on the chelation of the intact drugs with iron (II) in acetate buffer solution (pH5.6 ± 0.10) to form yellow colored chelates measured at 355 nm and 360 nm for EN and FL, respectively. Where good linearities were obtained in the range of 8-72 µg ml^-1 for EN and 16-80 µg ml^-1 for FL.
The second method depends on the measurement of the difference absorbance (ΔA) of each drug between 0.IM HCI and 0.1 M NAOH solutions at 283 nm for EN and at 346 nm for FL. Beer's law was obeyed in the range of 2-16 µg ml^-1 for EN and 4-32µg ml^-1 for FL. In the third one, EN and FL are determined using first derivative (¹D) and second derivative (²D) spectrophotometric techniques at 288 nm and 263 nm in the ranges of 10-22 µg ml^-1 and 8-24 µg ml^-1, respectively.
The intraday and interday precision (RSD %) were ranged between 0.16 and 2.45% for EN and FL. EN and FL can be determined in presence of up to 75% and 70% of their degradates via their iron (II) chelates, up to about 73% and 35%, respectively through the ΔA technique and up to about 65% by derivative spectrophotometry.
They were also successfully determined in their pharmaceutical formulations with mean percentage recoveries ± RSD ranged between 99.9-100.6±0.44-1.33% for EN and between 99.9-100.5±0.44-1.18% for FL.