Determination of N,N-dimethylaniline in penicillins by GC-MS

A quantitative GC-MS spectrometric assay was used for the determination of residual N,N-dimethylaniline as a contaminant in commercial penicillin derivatives from various sources. The assay utilizes selective ion focusing to monitor in a GC effluent the molecular ions of DMA generated by electron impact ionization. This method includes dissolution of the sample in alkaline solution, extraction of organic base with cyclohexane and injection into GC-MS with a 3% OV-17 column. Levels of 50 ppb of DMA were easily measured with a coeffecient of varation less than 5% and recoveries from spiked samples exceeded 97%. The results of the determinations of DMA in various commercial penicillins were relatively free of this contaminant.