Development and application of a capillary electrophoresis based method for the simultaneous screening of six antibiotics in spiked milk samples

An easy to use and low time consuming capillary electrophoresis (CE) method was developed and applied to the simultaneous determination of six antibiotics (ampicillin, amoxicillin, cloxacillin, penicillin, tetracycline and chloramphenicol) in spiked milk samples. Samples of milk were cleaned up by solid-phase extraction (with a C18 cartridge) after protein precipitation. Analysis was performed by CE and results compared with the obtained via HPLC, both coupled to a UV–vis detector (210 nm). CE employed a 58.5 cm long fused-silica capillary (50 cm to detector), 75 μm i.d., a 2.7 × 10−2 M KH2PO4, 4.3 × 10−2 M Na2B4O7 separation buffer, pH 8; an applied voltage of 18 kV; a hydrostatic injection of 0.5 psi during 3 s; and a run temperature of 25 °C. Under the described conditions, amoxicillin was not separated by HPLC, while CE was able to separate, and, therefore, allow detection. Regardless of amoxicillin, comparable results were obtained by HPLC and CE. The average recoveries of antibiotics, from milk fortified at 2.5 and 5 μg/mL, was over 72% with R.S.D.s within 5%. Recovery levels were essentially dictated by the used SPE cartridge.