Differentiation and characterization of isomeric polychlorinated biphenyls by gas-liquid chromatography coupled with electron impact and chemical ionization mass spectrometry

Abstract

This report describes the utilization of gas-liquid chromatography coupled with chemical ionization and electron impact mass spectrometry for the characterization and isomeric differentiation of polychlorinated biphenyls (PCB's) from numerous sources. By a comparison of model compounds with very complex mixtures, one is able to gain significant information about the o,o′-chlorine interaction of PCB's as monitored by mass spectrometry. The abudance of the specific (M − Cl) + ion assisted greatly in the isomeric differentiation of dichloro-, hexachloro-, and heptachlorobiphenyls. Furthermore, by the indepth characterization by mass spectrometry of the Ullman reaction products formed in the preparation of 14C-labeled PCB′s, one may conclude that a very complex mixture of dichloro- and trichlorobiphenyls is formed from a specific pure isomeric iodomonochlorobenzene during the Ullman reaction. As revealed by the use of gas-liquid chromatography coupled with electron impact mass spectrometry, care must be exercised in choosing the type of organic synthetic reactions for the preparations of polychlorinated biphenyls which will be used for biological testing in order to minimize isomeric contamination.