Development of an analytical method for cephapirin and its metabolite in bovine milk and serum by liquid chromatography with UV-VIS detection and confirmation by thermospray mass spectometry.

Metabolites of the cephapirin beta-lactam antibiotic have not previously been reported in bovine milk. The principal metabolite was tentatively identified as desacetylcephapirin by liquid chromatography with UV-VIS photodiode array (LC/UV-VIS PDA), and liquid-chromatography-mass-spectrometric (LC-MS) detection. Synthetic desacetylcephapirin was prepared by incubation of cephapirin in bovine milk and serum at 37 degrees C. Also, a method for determining cephapirin in bovine milk and serum was developed. The detection limits for cephapirin and desacetylcephapirin were estimated to be 10 and 50 micrograms/kg, respectively, for LC/UV-VIS PDA, and 100 and 500 micrograms/kg for LC-MS.