Rapid and economical high-performance liquid chromatographic method for the determination of norfloxacinin serum using a microparticulate C-18 guard cartridge

A rapid and economical high-performance liquid chromatographic assay is described for norfloxacin in serum. Samples (100 mu l) containing N-ethylnorfloxacin as the internal standard were extracted into 1 ml of chloroform. Chromatography was performed at 30 degrees C on a 40 X 3.2 mm I.D. C-18 guard cartridge (3 mu m spherical particles) using a mobile phase of 11% (v/v) acetonitrile in 0.01 M phosphate buffer (pH 2.5) containing 0.001 M triethylamine, and pumped at 1 ml/min. Detection was at 279 nm. The retention times of norfloxacin and internal standard were 1.9 and 2.9 min, respectively. Calibration curves were linear (r > 0.999) from 0.1 mg/l to at least 2.0 mg/l. Within-day and between-day precision (C.V.) were 8.6% or less, and accuracy was 5.3% or less. Absolute assay recovery of norfloxacin was over 70%.