Determination of enrofloxacin and its metabolite ciprofloxacin in goat milk by high-performance liquid chromatography with diode-array detection. Optimization and validation.

A high-performance liquid chromatography-diode array detection method (HPLC-DAD) combined with liquid chromatography-mass spectrometry was developed for the determination of enrofloxacin and its metabolite ciprofloxacin in goat milk. The HPLC-DAD method validation was compliant with the "DG SANCO 1805/2000" European regulation. The residues were extracted from milk with phosphate buffer, purified on a C18 Speedisk cartridge SPE (Baker) and then analysed using HPLC-DAD set at 277 nm. The decision limit (CCa) calculated by spiking samples at 100 microg/kg with both analytes, taking into account the maximum residue limit (MRL) of 100 microg/kg established by the European Union for the sum of enrofloxacin and its metabolite ciprofloxacin in milk, was 105.3 microg/kg for enrofloxacin and 105.5 microg/kg for ciprofloxacin. The detection capability (CCbeta) was 110.7 and 110.9 microg/kg for enrofloxacin and ciprofloxacin, respectively. The mean recoveries of the method, calculated by spiking samples at 50, 100 and 150 microg/kg were 84% for enrofloxacin and 88% for ciprofloxacin. The limit of quantification was 20 microg/kg for both analytes. The HPLC-DAD validated method was successfully applied for the first time in goats milk, and proved to be suitable for the sensitive and accurate quantification and confirmation analysis of enrofloxacin and ciprofloxacin for regulatory purposes.