Improvement in the multiresidue liquid chromatographic analysis of residues of mono- and dibasic penicillins in bovine muscle tissues.

A recently developed multiresidue method using gradient liquid chromatographic conditions for analysis of residues of beta-lactam drugs in bovine muscle tissues after precolumn derivatization with acetic anhydride was modified to permit isocratic analysis. The modification included replacing the acylating reagent, acetic anhydride, with benzoic anhydride and increasing sample size for extraction from 2 to 3 g. The modifications have reduced analysis time per sample from > 1 h to about 22 min without loss in detection sensitivities for the beta-lactams, resulting in a significant increase in the number of samples that can be analyzed in 1 day from 1 to 8. The modifications make the multiresidue LC method more suitable than the original method for use in regulatory programs for routine analysis of these veterinary drug residues in bovine muscle tissues.