The replacement of trideuteromethyl by methyl groups when using methane as a reagent gas in chemical ionization mass spectrometry.

The methane chemical ionization spectra of a number of tertiary and quaternary amines with a N-trideuteromethyl group show substitution of this group by methyl. The isotopic purity of the original amines was shown to be greater than 99% using ammonia as a reagent gas.