STUDIES IN CHEMICAL-IONIZATION .28. ANALYSIS OF BENZANNELATED THIOPHENE DERIVATIVES BY NEGATIVE-ION CHEMICAL-IONIZATION USING OXYGEN AS A REAGENT GAS

Under the conditions of negative-ion chemical ionization with O-2 as a reagent gas [NCI(O-2)], thiophene derivatives suffer surface-catalyse d oxidative degradation with subsequent ionization of the resulting sp ecies. These degradation reactions are to some extent structure specif ic and thus may be used for the localization of rings and/or substitue nts. It is advisable, however, to combine NCl(O-2) with either electro n impact ionization or positive ion Cl. The latter ionization methods yield abundant M(+.) ions but hardly any structure-specific fragments, whereas with NCl(O-2) the determination of the molecular mass may be difficult owing to the competing oxidation reactions.