Abstract: Micellar electrokinetic capillary chromatography (MECC) coupled with the addition of methanol to the running buffer was used for the separation and determination of five β-lactam antibiotics, ceftiofur, cephazoline, cephalexin, ampicillin and penicillin G. The running buffer was optimized to consist of 20 mmol/L Na2HPO4, 20 mmol/L NaH2PO4 (pH 8.5), 20 mmol/L SDS and 0.25 (V/V) methanol. Under the voltage of 18 kV, baseline separation was achieved for the five antibiotics within 15 min, and their concentrations and peak areas exhibited a good linear relationship. The detection limits for these antibiotics were between 5.3 and 8.1 mg/L. The precision of the method was found to be 3.8%－5.5%. The results indicate that the combination of micellar pseudostationary phase and organic additives enables highly efficient chromatographic separation of antibiotics of very similar structures.

Key words: micelle capillary electrophoresis, organic additive, β-lactam antibiotics, baseline separation