STRUCTURES OF THE ADDUCT IONS FORMED IN THE AMMONIA CHEMICAL-IONIZATION OF KETONES

The low-energy and high-energy collision-induced dissociation (CID) ma ss spectra of the adduct ions M.NH4+, M.(CH3NH2)H+, M.((CH3)2NH)H+, an d M.((CH3)3N)H+ (M = acetone and 3-pentanone) as well as the CID mass spectra of the higher adducts M2(NH3)H+, M2(CH3NH2)H+, M(NH3)2H+, M(CH 3NH2)2H+,and M((CH3)2NH)2H+ (M = 3-pentanone) have been determined. Th e low-energy CID mass spectra of the adducts containing a single molec ule of the ketone and the amine show only formation of the protonated amine on fragmentation, consistent with a proton-bound cluster ion str ucture. The high-energy CID mass spectra show formation of the protona ted amine but also fragmentation by elimination of a neutral amine and neutral amine plus H, presumably representing fragmentation of very h ighly excited ions. The fragmentation modes of the ions containing two molecules of the amine or two molecules of the ketone also are consis tent with proton-bound cluster ion structures.