Chemical ionization mass spectrometry of N-methylcarbamate insecticides, some of their metabolites, and related compounds.

The chemical ionization (CI) mass spectra with methane as the reagent gas are reported for 25 N-methylcarbamate insecticides or related compounds. The [M + 1]+ ions in the CI spectra are larger than the parent ions in the corresponding electron impact (EI) spectra of N-methyl- and N,N-dimethylcarbamates, but the contrary is true with N-hydroxymethylcarbamates. CI but not EI fragmentation of substituted-phenyl N-hydroxymethylcarbamates [ROC (O) NHCH2OH] appears to involve a 4-membered [ROC(O)NHCH2]+ intermediate which rearranges to give a [ROCH2]+ fragment. Other fragmentations unique to the CI spectra are also discussed.