Determination of penicillin G residues in edible animal tissues by liquid chromatography.

An improved method has been developed for the determination of benzyl penicillin in animal tissues. Tissues are fortified with a known amount of penicillin V (internal standard) and extracted with water. The extract is deproteinized with sulfuric acid and sodium tungstate, filtered, and concentrated on a conditioned C18 solid phase extraction column. Penicillin V and benzyl penicillin are then eluted from the column with 1 mL 60% acetonitrile-35% water-5% 0.2M phosphate buffer solution and derivatized with 1 mL 1,2,4-triazole-mercuric chloride solution at 65 degrees C for 30 min. An aliquot of this sample is analyzed by reverse phase liquid chromatography with UV detection at 325 nm. The limit of detection is 5 micrograms/kg (ppb) penicillin G (8.4 IU/kg) in liver, kidney, and muscle tissues).