[Use of the penicillanic acid formation reaction for the analysis of penicillins. The quantitative determination of oxacillin].

A procedure for quantitative determination of oxacillin by means of spectrophotometry is described. The procedure is based on the capacity of penicillins to transform on heating in acid buffer solutions containing copper ions into respective penicillenic acids having specific absorption characteristics in the UV-spectrum region. The amount of oxacillin was estimated by the optical density of the solutions at a wave length of 335 nm corresponding to the absorption maximum of the penicillenic acid of oxacillin. The optimal conditions for the reaction of the penicillenic acid formation, i.e. pH of the buffer solution and the level of the copper ions in it, time and temperature of heating were determined. The data on the comparison of the specificity and reproducibility of the new method with the currently used ones for determination of oxacillin are presented.