GLC determination of N,N-dimethylaniline in penicillins

A reliable GLC procedure was developed for the determination of residual N,N-dimethylaniline as a contaminant in ampicillin commerical samples from various sources. The procedure was similarly applied to other penicillins and cephalosporins. The method involves dissolution of the sample in aqueous alkali, extraction of the organic base with cyclohexane containing naphthalene as an internal standard, and injection into gas chromatograph with a phenyl methyl silicone column. Levels of 0.1 ppm of dimethylaniline were easily measured with a coefficient of variation less than 10%, and recoveries from spiked samples exceeded 99%.