A simple sample treatment for the determination of enrofloxacin and ciprofloxacin in raw goat milk

A solid-phase extraction (SPE) procedure requiring no prior protein precipitation for the determination of enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) in goat milk with fluorescence detection (FD) was developed. Octadecyl (C18), ethyl (C2), cyclohexyl (CH) and phenyl (PH) sorbents were initially tested for this purpose. The influence of the loading variables affecting the extraction efficiency (viz. breakthrough volume and eluent composition/volume) was examined. Using C18 cartridges in combination with 5 mL of H2O (containing 2% TFA)/acetonitrile (ACN)/methanol (MeOH)/(77:15:8, v/v/v) as eluent was found to provide the best recoveries and highest efficiency. This sample preparation method provided absolutely clean extracts with recoveries up to 99.7% for ENR and 95.9% for CIP. The overall chromatographic running time was 6 min, and the retention times for ENR and CIP were 5.32 and 4.25 min, respectively. The analytical response was linear over the concentration range from 10 to 50 μg L− 1 for ENR and CIP, with a correlation coefficient (r) of 0.998 for ENR and 0.997 for CIP. The method was validated and applied to real goat milk samples where the analytes (ENR and CIP) were natively present in the matrix since they were obtained from ENR-treated animals. Using SPE to treat the samples expedites the process in relation to most available methods for the same purpose, which involve time-consuming extraction and clean-up of ENR and CIP from milk samples.