Fluoroquinolone antibiotic determination in bovine, ovine and caprine milk using solid-phase extraction and high-performance liquid chromatography-fluorescence detection with ionic liquids as mobile phase additives

This paper describes the use of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIm-BF4) as mobile phase additive for the analysis by high-performance liquid chromatography with fluorescence detection of a group of seven basic fluoroquinolone antibiotics (i.e. fleroxacin, ciprofloxacin, lomefloxacin, danofloxacin, enrofloxacin, sarafloxacin and difloxacin) in different milk samples. EMIm-BF4 was found superior to 1-butyl-3-methylimidazolium tetrafluoroborate for the separation of the analytes from chromatographic interferences of the sample matrix. The optimized method was applied to the analysis of ovine, caprine and bovine milk, in the last case in either skimmed, semi-skimmed and full-cream milk after suitable acidic deproteination followed by a solid-phase extraction procedure. Recovery values between 73% and 113% were obtained for the three types of bovine milk samples, as well as for ovine and caprine milk (RSDs below 16% in all cases), which clearly demonstrates the applicability of the method to the three types of milk irrespective of the fat content of the samples. Limits of detection were in the range of 0.5–8.1 μg/L (approximately 0.5–25.9 μg/kg), well below the maximum residue limits established for these compounds by the current European legislation. A screening study of 24 different milk samples was also developed. In none of the samples, residues of the selected antibiotics were found.