Positive chemical ionization mass spectra of polycyclic chlorinated pesticides

Methane chemical ionization (CI) mass spectra for a series of ten polycyclic chlorinated insecticides and metabolites have been examined. In all cases except heptachlor epoxide the base peak corresponded to elimination of Cl, or OH from the molecule ion. In the spectrum of heptachlor epoxide the [M + H]⁺ and [M ? Cl]⁺ clusters were of approximately equal intensity. The CI spectra were remarkably simple, invariably less complex than the corresponding electron-impact (EI) mass spectra and the intensity of the ions with high information content, e.g. [M ? CI]⁺ was uniformly high. All of these features are important to the analytical potential of these studies. Retro Diels-Alder (RDA) fragments were observed for the chlordanes, aldrin, isodrin, nonachlor and heptachlor epoxide. The reported preliminary data suggest that the relative intensity of RDA ions in CI mass spectra may be useful in establishing molecular configurations.