Compound-Specific Carbon Isotopic Analysis of Aroclors, Clophens, Kaneclors, and Phenoclors

Abstract

Advances in instrumentation have allowed the measure ment of the isotopic composition of 13C/12C (δ13C) in the effluent of a gas chromatograph for each individual peak; this technique is called compound-specific isotope analysis (CSIA). CSIA has been used in a variety of biogeochemical studies to determine the sources of hydrocarbons. We have utilized the technique of CSIA to examine δ13C of the individual congeners in the polychlorinated biphenyl (PCB) mixtures Aroclor 1242 and 1254; Clophen A30, A50, and T241; Kanechlor 200, 300, 400, 500, and 600; and Phenoclor DP-3, DP-4, DP-5, and DP-6. In addition, the bulk δ13C values (i.e., the entire mixture) were determined for comparison to the CSIA values. Bulk δ13C values ranged from −22.34‰ (Phenoclor DP-3) to −26.95‰ (Clophen A30). The analogues Aroclor 1254, Clophen A50, Kanechlor 500, and Phenoclor DP-5 had different bulk δ13C values. The bulk values fall within the CSIA values and are similar to the average of the δ13C values of the individual congeners. In both the bulk δ13C analysis and the CSIA, the PCBs show increased 13C depletion with increasing chlorine content. Values for congeners within a PCB mixture also showed a wide range of δ13C isotope values; for example, δ13C values in the Kanechlor 600 mixture range from −18.65‰ (PCB 52) to −27.98‰ (PCB 180). Large differences in δ13C values for individual congeners between mixtures were found (e.g., PCB congener 52, Clophen A30−28.35‰ vs Kanechlor 600−18.65‰). The δ13C values for individual congeners in the PCB mixtures showed a similar pattern of 13C depletion with increasing chlorine content, this trend is probably a result of kinetic isotope effects caused by the position of the chlorine atom on the biphenyl molecule. The wide range in δ13C ratios between PCB mixtures and individual congeners may prove to be a powerful tool in the determination of sources of PCBs in the environment, and this technique may have wide applications in environmental chemistry.