A reverse-phase HPLC assay for the simultaneous determination of enrofloxacin and ciprofloxacin in pig faeces

Abstract A reverse-phase HPLC assay is described for the simultaneous assay of enrofloxacin (ENR) and ciprofloxacin (CPX) in pig faeces. Extraction used dichloromethane, 2-propanol and 0.3 M ortho -phosphoric acid (1:5:4 v/v/v). Separation was achieved using a Spherisorb S5 C8 column, heated to 50 °C and a mobile phase of 0.16% ortho -phosphoric acid (adjusted to pH 3.0 with tetrabutylammonium hydroxide solution) with 20 ml acetonitrile per litre solution. The method used fluorescence detection (Ex 310 nm; Em 445 nm), a flow rate of 1 ml/min and a 20 μl injection volume. Retention times were approximately 6 min for ciprofloxacin and 10 min for enrofloxacin. The linearity range for both compounds was 0–20 mg/kg, lowest limit of quantification 0.3 mg/kg and recoveries were >92%.