Factors considered in the development of a method for the determination of toxic, water-soluble benzidines, involved providing a good technique for their adequate recovery, converting quantitatively the isolated amines to relatively stable derivatives suitable for measurement and storage, coupled with relative ease of preparation of the derivatives, and resolving the prepared compounds during their measurement. Benzidine and dichlorobenzidine are quantitatively extracted from wastewater and measured quantitatively through the preparation of their respective pentafluoropropionamides (PFP) by using PFP-imidazole. Overall recovery efficiency for benzidines from wastewater ranges from 91 to 103%. These derivatives are relatively stable compounds and have detection limits of 0.2 pg or less, when electron capture detection is used with gas chromatograpy. Derivatives of o-tolidine and dianisidine are also described.