SELECTIVE ADDUCT FORMATION BY DIMETHYL ETHER CHEMICAL IONIZATION IN A QUADRUPOLE ION TRAP MASS-SPECTROMETER AND A CONVENTIONAL ION-SOURCE

Dimethyl ether is evaluated as a selective chemical ionization reagent for mono- and bisubstituted oxyaromatic compounds. The relative abundance and variety of adducts formed under chemical ionization conditions in a conventional ion source and in a quadrupole ion trap mass spectrometer are compared, and adduct ions are characterized by using collision-activated dissociation. Dimethyl ether ions demonstrate both functional group and positional selectivity upon reaction with the aromatic compounds in the quadrupole ion trap. The positional selectivity is attributed to substituent effects. This selectivity is not observed when a conventional chemical ionization source is used to form the adducts. Overall, adduct ions are of greater abundance in the conventional ion source than in the low-pressure environment of the quadrupole ion trap mass spectrometer.