Infrared multiphoton dissociation of electrosprayed crown ether complexes

Abstract

Complexes of 18-crown-6, 15-crown-5, and 12-crown-4 with Na +, K +, Rb +, Cs + and H 3O + were observed and characterized using infrared multiphoton dissociation (IRMPD) in conjunction with Fourier transform ion cyclotron resonance mass spectrometry. The complexes were formed in methanol-water solution and were subsequently transported into the gas phase using two different electrospray ionization sources. Trapped complexes were dissociated utilizing IRMPD to obtain fragmentation and binding information on selected crown ether complexes. Dissociation of crown ether-alkali metal complexes proceeded via the loss of the alkali metal ion at low laser fluences; dissociation of the crown was not observed. For all of the alkali metal-crown ether complexes investigated, it was found that Na + binds to the crown ether more strongly than any of the larger alkali metal ions. In contrast to the alkali metal complexes, IRMPD of (18-crown-6)H 3O + proceeded via loss of H 2O to produce protonated 18-crown-6 ions. At higher laser fluences, (15-crown-5)H 3O + and (12-crown-4)H 3O + lost water and then fragmented by sequential loss of C 2H 4O units.