A new spectrophotometric method for the determination of penicillins

Abstract A rapid and convenient method is described for the determination of nine commonly used penicillins. This is based on the spectrophotometric measurement at 325–345 nm of penicillenic acid mercuric mercaptides of the penicillins, formed in quantitative yield on heating at 60° or on standing at 20° in a 1·2 m imidazole and 10−3 m mercuric chloride solution at pH 6·8. The method, which permits detection of concentrations of penicillins down to 0·5 μg/ml, is reproducible. Since the intact penicillin molecule is required for the penicillenic acid formation, the method is highly specific and useful as a means of assessing stability.