Aqueous in situ derivatization of carboxylic acids by an ionic carbodiimide and 2,2,2-trifluoroethylamine for electron-capture detection

We report a technique for the rapid, room temperature derivatization of aqueous carboxylic acids to the corresponding 2,2,2-trifluoroethylamide derivative. 3-Ethyl-1-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC) and 2,2,2-trifluoroethylamine hydrochloride (TFEA) were added to aqueous samples of several acids of interest in environmental analytical chemistry, including benzoic acid, ibuprofen, clofibric acid, monochloroacetic acid, dicholoroacetic acid, bromoacetic acid, monochlorophenoxy acetic acid, dichlorophenoxy acetic acid, trichlorophenoxy acetic acid, acetylsalicylic acid, and cholorobenzoic acid. Amidization was essentially complete within ten minutes, and subsequent liquid–liquid extraction of the amides with methyl tert-butyl ether (MTBE) demonstrated recoveries of over 85%. The starting materials, both quaternary ammonium salts, were not co-extracted with the derivative, yielding much cleaner samples than historically obtained from carbodiimide based techniques. The fluorinated amides produced had excellent chromatographic characteristics for gas chromatography and were easily detected by electron-capture detection (ECD) or electron impact mass spectrometry. This method is suggested as a sensitive alternative to more traditional acidification, extraction, and ex situ derivatization techniques.