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 C(18) cartridge) after protein precipitation. Analysis was performed by CE and results compared with the obtained via HPLC, both coupled to a UV-vis detector (210nm). CE employed a 58.5cm long fused-silica capillary (50cm to detector), 75microm i.d., a 2.7x10(-2)M KH(2)PO(4), 4.3x10(-2)M Na(2)B(4)O(7) separation buffer, pH 8; an applied voltage of 18kV; a hydrostatic injection of 0.5psi during 3s; and a run temperature of 25 degrees 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 5microg/mL, was over 72% with R.S.D.s within 5%. Recovery levels were essentially dictated by the used SPE cartridge.