Regioselectivity of the oxygen addition-induced dechlorination of PCBS and DDT metabolites in electron capture mass spectrometry

The electron capture mass spectra of 28 35Cl-labeled polychlorinated biphenyls (PCBs) and 4 37Cl-labeled 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) metabolites were obtained by using a 20% oxygen in methane mixture as the reagent gas. The degree of regioselectivity of the PCB oxygen addition-induced dechlorination reaction was determined by measurement of the residual amount of label in the M-19 ions produced by addition of O2 and subsequent loss of OCl from the molecule. Chlorine was lost in a random manner from the PCBs, contrary to the dechlorination reaction observed when methane alone was used. For the DDT metabolites, many dechlorination reactions were observed in addition to the one that generated the M-19 ions. Loss of Cl, loss of Cl2, and addition of O2 with the loss of one or two HCl molecules also were seen. These various dechlorination reactions involved only the aliphatic chlorines. Addition of O2 followed by loss of Cl at the beta position of 2,2-bis(4-37Cl-chlorophenyl)-1-chloroethylene and 2,2-bis(4-37Cl-chlorophenyl)-1,1-dichloro-ethylene may be due to the ability of the diphenyl methane moiety to stabilize the intermediates. Formation of an ion that corresponds to 4,4′-dichlorobenzophenone also was observed for three of these labeled DDT metabolites. (J Am Soc Mass Spectrom 1996, 7, 66–72