DECHLORINATION OF POLYCHLORINATED-BIPHENYLS IN ELECTRON-CAPTURE NEGATIVE-ION CHEMICAL-IONIZATION MASS-SPECTROMETRY

The electron-capture negative-ion chemical ionization mass spectra of 36 Cl-35 mono- and di-labelled penta- and hexachlorobiphenyls were stu died. Under the conditions of the analyses, the dechlorination of thes e congeners probably proceeds through electrophilic hydrogen atom atta chment followed by rapid loss of the chlorine atom at the same positio n. These dechlorination reactions occur regioselectively. When present , ortho-chlorines are lost preferentially to meta- and para-chlorines. The extent of the dechlorination reaction, as seen by the relative ab undance of the [MH - Cl]- ions, decreases with increasing number of or tho-chlorines.