Analysis of penicillin and its β-lactamase hydrolysis products in milk using capillary zone electrophoresis

A capillary zone electrophoresis method was established for simultaneous analysis of penicillin G and penicillin acid in milk. Milk samples were deproteinized and the analytes were extracted with acetonitrile. Separation of target compounds was performed through electrophoresis. Under optimum conditions, the proposed method demonstrated good correlation coefficients (R > 0.9953), precision (<6.2%), accuracy (89.2–96.8%), and limits of detection and quantification of penicillin G and penicillin acid (LOD, 0.01 and 0.5 μg mL−1, LOQ, 0.04 to 1.7 μg mL−1, respectively). The proposed method for the determination of penicillin and penicillin acid in milk is rapid, convenient and low-cost, and can measure β-lactamase activity in milk. The thermal stabilities of penicillin G, penicillin acid, and β-lactamases in milk were satisfactory when the temperature was lower than 303 K. When the temperature was higher than 353 K for 5 h, β-lactamase tended to be inactivated completely. When the temperature was 373 K, penicillin G and penicillin acid were easily degraded.