Fluorometric determination of cephradine in plasma

A fluorometric method was developed for the determination of cephradine in plasma. A fluorescent product is formed when samples of deproteinized plasma containing cephradine are heated for 3 hr at 100 degrees and pH 1. The fluorescence is determined in sodium hydroxide solution (pH 13.5) at excitation and emission wavelengths of 350 and 445 nm, respectively. Only 0.1 ml of plasma is required, and concentrations of cephradine as small as 0.1 mug/ml may be determined. In plasma samples from a dog taken over a 10-hr period after an intramuscular injection of 250 mg of cephradine, essentially similar concentrations of cephradine were obtained by the fluorometric method and a standard microbiological bioassay.