Determination of penicillins in animal tissues at trace residue concentrations: II. Determination of amoxicillin and ampicillin in liver and muscle using cation exchange and porous graphitic carbon solid phase extraction and high-performance liquid chromatography.

A method for the determination of the basic penicillins, amoxicillin and ampicillin, in animal tissue is described. The method used aqueous extraction with tungstate to remove proteins followed by cation exchange solid phase extraction (SPE) clean-up. This extract was further purified using porous graphitic carbon (PGC) SPE. Extracted residues were derivatized with acetic anhydride followed by triazole/mercuric chloride prior to reversed phase HPLC with UV determination at 325 nm. At the Maximum Residue Limit of 50 micrograms/kg in fortified cattle muscle validation gave mean recoveries for amoxicillin of 57% and 50% on two different days with relative standard deviations of 19% and 15% respectively. For ampicillin the recoveries were 72% and 59% with relative standard deviations of 15% and 19% respectively.