Molecule/radical reactions prior to ionization under negative chemical ionization conditions

It is shown that alkyl radical species present in CH 4 or iso ‐C 4 H 10 plasma can react with substrate molecules to give [M+C n H 2n ] species. These species become evident especially in negative chemical ionization as [M+C n H 2n ] −˙ and, less obviously, in positive chemical ionization as [M+C n H 2n+1 ] + ions which, for example in natural products chemistry, may be mistaken for a series of homologous compounds present in the sample.