Determination of Penicillin G in Beef and Pork Tissues Using an Automated LC Cleanup

A procedure previously described for determination of β-lactam antibiotics in milk was modified for use with tissues. Tissues were extracted directly with acetonitrile (procedure I) to avoid degradation of penicillin G in water homogenates. Recovery of penicillin G in acetonitrile extracts of tissues was improved by addition of tetraethylammonium chloride and, in some cases, pH adjustment. The acetonitrile extracts were concentrated by evaporation and filtered. For cleanup, an automated high-performance liquid chromatography (HPLC) fractionation was used. The fraction corresponding to penicillin G was tested by a rapid screening test and, if positive, was analyzed by HPLC. For analysis, an Inertsil ODS-2 column was used with a mobile phase of 0.0067 M KH 2 PO 4, 0.0033 M H 3 PO 4 −acetonitrile (68 + 32) with UV detection at 215 nm. For confirmation by treatment with β-lactamase, tissues were homogenized in water. An aliquot of the water homogenate was treated with β-lactamase prior to extraction with acetonitrile and tetraethylammonium chloride (procedure II). Recoveries were 66−95% in the 0.1−1.0 ppm range, depending on the tissue, with a detection limit of about 5 ng/g.