A direct liquid chromatographic quantitation of ciprofloxacin in microsamples of plasma with fluorometric detection.

We describe a rapid liquid chromatographic assay for ciprofloxacin in 20-50 microliter samples of plasma by use of C18 cartridge in conjunction with a radial compression system and a C18 precolumn module. The mobile phase consisted of an ammonium phosphate solution (pH 2.5), acetonitrile, and methanol. The sample was diluted with an equal volume of water and directly injected into the cartridge. The drug and internal standard (quinine bisulfate) were detected spectrofluorometrically. The peak height ratio (PHR) varied linearly with concentration (0.05-4 micrograms/ml), and the coefficient of variation of the PHR did not exceed 5%. No interference for any endogenous substance or other concomitantly used drug in the assay was detected. This method is currently being used to monitor ciprofloxacin in patients treated with this drug for brucellosis.