Methane‐oxygen enhanced negative ion mass spectra of polychlorinated diphenyl ethers

Methane‐oxygen enhanced negative ion mass spectra of 15 chlorinated diphenyl ethers contained some combination of [M] − ˙, [M ‐ 1] − , [M − 19] − , [M − 36] − , [M − 55] − , and [M + 35] − anions. The relative abundances of these ions are related to the chlorine substitution pattern. Similar ions appear in the negative ion spectra of polychlorinated anisoles. The study of known isomers of polychlorinated model compounds extends the utility of the negative ion method in the analysis of polychlorinated aromatics such as polychlorinated biphenyls, dioxins and furans. The spectra were shown to be very dependent on the temperature of the ion source; a temperature change of 25°C was shown to have pronounced effects. Spectral variation with temperature has implications for computer library searches, ultimate sensitivity limits and analysis in the presence of interfering isobaric ions.