[Simultaneous determination of four beta-lactam antibiotics in milk by solid-phase extraction-micellar electrokinetic chromatography].

A solid-phase extraction (SPE)-micellar electrokinetic chromatography (MEKC) method was developed for the simultaneous determination of four beta-lactam antibiotics (ampicillin, amoxicillin, penicillin V and cephalexin) in spiked milk samples. The milk samples were extracted by SPE after protein precipitation. The analysis was performed by MEKC at 18 kV with phosphate buffer containing sodium dodecyl sulfate (SDS) and the detection was carried out at 210 nm. The four antibiotics could be baseline-separated less than 9 min. The linearities in 0.5 - 20 mg/L could be constructed with the correlation coefficients between 0.994 3 - 0.997 6, and the limits of detection were 0.16 - 0.20 mg/L. The average recoveries of antibiotics from milk were over 70% except amoxicillin. The method is sensitive, specific and easy for the determination of beta-lactam antibiotic residues in milk.