Development and application of a capillary electrophoresis–electrochemiluminescent method for the analysis of enrofloxacin and its metabolite ciprofloxacin in milk

Enrofloxacin (ENR) is a fluoroquinolone developed exclusively for the use in veterinary practice for the treatment of respiratory and gastrointestinal infections, and ciprofloxacin (CIP) is its main active metabolite. Their contents are regulated by the EU Council Regulation no. 2377/90 in animal edible tissues. We developed a sensitive and rapid method for the determination of ENR and CIP by capillary electrophoresis (CE) with electrochemiluminescence (ECL) detection. The method is based on the detection of aliphatic tertiary or secondary amino moieties in ENR and CIP with end-column tris(2,2-bipyridyl)ruthenium(II) electrochemiluminescence. Parameters that affect separation and detection were optimized. Under the optimized conditions, the calibration functions were linear in the range of 0.03–1 μg ml−1 for ENR and 0.05–1.2 μg ml−1 for CIP. The detection limits of ENR and CIR were 10 ng ml−1 and 15 ng ml−1, respectively, based on the signal-to-noise ratio of 3. The relative standard derivations of the peak height and the migration time for ENR and CIP were less than 4.13%. The developed method was successfully applied to determine ENR and CIP in milk with a solid-phase extraction procedure.