The procedure is based on acidic, basic, and neutral impurities introduced from the coca plant and from the processing of cocaine in clandestine laboratories. It examines benzoic acid, anhydroecgonine methyl ester, anhydroecgonine, trans-cinnaminic acid, ecgonine methyl ester, ecgonine, tropacocaine, benzoylecgonine, norcocaine, beta-truxinic acid, alpha-truxillic acid, cis-cinnamoyl ecgonine methyl ester, trans-cinnamoyl ecgonine methyl ester, and N-formyl cocaine as a multiple peak chromatogram obtained by flame ionization detection (FID) capillary gas chromatography for comparison purposes. Impurities containing either alcoholic, N-nor, or carboxylic acid functional groups were analyzed as their silyl derivatives. This procedure computed the averages and standard deviations of the concentration measurements from the 13 impurity variables obtained from 368 randomly chosen separate batches. Exhibits of common batch origin could be determined and gave identical chromatographic profiles, while profiles were found to be unique of separate batches. This analytical procedure provides the forensic chemist with a method to determine batch to batch differences in cocaine samples. 7 figures, 3 tables, and 60 references (Author abstract modified)