Analysis of Six ß-Lactam Residues in Milk and Egg by Micellar Electrokinetic Chromatography with Large-Volume Sample Stacking and Polarity Switching.

A new micellar electrokinetic chromatography method with large-volume sample stacking and polarity switching was developed to analyze amoxicllin, cephalexin, oxacillin, penicillin G, cefazolin, and cefoperazone in milk and egg. The important parameters influencing separation and enrichment factors were optimized. The optimized running buffer consisted of 10 mM phosphate and 22 mM SDS at pH 6.7. The sample size was 1.47 kPa × 690 s, the reverse voltage was 20 kV, and the electric current recovery was 95%. Under these optimum conditions, the enrichment factors of six ß-lactams were 193-601. Their LODs were <0.26 ng/g, and LOQs were all 2 ng/g, which was only 1/50-1/2 of the maximum residual limits demanded by U.S. and Japanese regulations. The intraday and interday RSDs of method were lower than 3.70 and 3.91%, respectively. The method can be applied to determine these six antibiotic residues in egg and milk.

Determination of five quinolone antibiotic residues in foods by micellar electrokinetic capillary chromatography with quantum dot indirect laser-induced fluorescence.

A new assay was developed for the determination of five quinolone antibiotic residues in foods, loxacin, enrofloxacin, ciprofloxacin, lomefloxacin, and norfloxacin, by micellar electrokinetic capillary chromatography with indirect laser-induced fluorescence, in which cadmium telluride quantum dots were used as a fluorescent background substance. Some factors that affected the peak height and the resolution were examined. The optimized running buffer was composed of 20 mM SDS, 7.2 mg/L quantum dots, and 10 mM borate at pH 8.8. The separation voltage was 20 kV. Under these conditions, five quinolone antibiotic residues were separated successfully within 8 min. The detection limits ranged from 0.003 to 0.008 mg/kg; the linear dynamic ranges were all 0.01 ∼ 10 mg/kg; and the average recoveries of the spiked samples were 81.4 ∼ 94.6 %. The assay can meet the requirement of maximum residue limits to these five quinolone antibiotics in the regulations of the European Union and Japan and has been applied for determining their residues in animal-derived food.