Spectrophotometric determination of penicilloates in penicillins

A procedure has been developed for the determination of penicilloates based on the reduction of CuII and detection of CuI using neocuproine. The sensitivity range is 5.6-56 microns penicilloate and the standard deviation was found to be between 1 and 2%. All the penicilloates tested reduced CuII under the conditions of the assay and a slight modification allowed a reasonably accurate determination of the level of this biologically inactive ingredient in a mixture with the parent penicillin. The deterioration of solutions of benzylpenicillin was also studied.