An HPLC method for the determination of penicillin G residues in veal calf liver tissues

A method developed in our laboratory and used for several years for the routine determination of penicillin G residues in animal tissues by liquid chromatography failed when it was used in a recent study for the determination of penicillin G residues in liver tissues of 2- to 5-week-old veal calves. The method was, therefore, modified as follows to permit the determination of penicillin G residues in liver tissues from very young calves. Penicillin G was extracted from calf liver tissue with acetonitrile instead of water. The acetonitrile extract was evaporated to near dryness, and the resulting residue was dissolved in 30 mL of 2% sodium chloride and cleaned up on a t-C-18 Sep-Pak cartridge. The retained penicillin was then eluted with 1 mL of 60% acetonitrile/35% water/5% 0.2 M phosphate buffer solution, derivatized with 1 mL of 1,2,4-triazole/mercuric chloride solution at 65 degreesC for 30 min, and analyzed by reverse-phase liquid chromatography with ultraviolet detection at 325 nm. The limits of detection and quantitation for this method are 1.5 and 5 ng/g, respectively, for penicillin G.