REGIOSELECTIVITY OF THE OXYGEN ADDITION-INDUCED DECHLORINATION OF PCBS AND DDT METABOLITES IN ELECTRON-CAPTURE MASS-SPECTROMETRY

The electron capture mass spectra of 28 Cl-35-labelcd polychlorinated biphenyls (PCBs) and 4 Cl-37-labeled 1,1,1-trichloro-2,2-bis(p-chlorop henyl)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 produ ced by addition of O-2 and subsequent loss of OCl from the molecule. C hlorine was lost In a random manner from the PCBs, contrary to the dec hlorination 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 Cl-2, and addition of O-2 with the loss of one or two HCl molecules also were s een. These various dechlorination reactions involved only the aliphati c chlorines. Addition of O-2 followed by loss of Cl at the beta positi on of 2,2-bis(4-Cl-37-chlorophenyl)-1-chloroethylene and 2,2-bis(4-Cl- 37-chlorophenyl)-1,1-dichloroethylene 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.