A Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer has been installed at a free electron laser (FEL) facility to obtain infrared absorption spectra of gas phase ions by infrared multiple photon dissociation (IRMPD). The FEL provides continuously tunable infrared radiation over a broad range of the infrared spectrum, and the FT-ICR mass spectrometer, utilizing a 4.7 Tesla superconducting magnet, permits facile formation, isolation, trapping, and high-mass resolution detection of a wide range of ion classes. A description of the instrumentation and experimental parameters for these experiments is presented along with preliminary IRMPD spectra of the singly-charged chromium-bound dimer of diethyl ether ͑Cr͑C 4 H 10 O͒ 2 + ͒ and the fluorene molecular ion ͑C 13 H 10 + ͒. Also presented is a brief comparison of the fluorene cation spectrum obtained by the FT-ICR-FEL with an earlier spectrum recorded using a quadrupole ion trap (QIT).
Variation in the wavelength of irradiation in infrared multiple-photon dissociation (IR-MPD) of lithium-tagged glucose-containing disaccharide ions (1-2-, 1-3-, 1-4-, and 1-6-linked isomers of both anomeric configurations) resulted in marked differences in their mass spectral fragmentation patterns. Two-dimensional plots of the fragment yield versus infrared wavelength for each mass spectral product ion were unique for each isomer and can be considered a spectral fingerprint. Individual product ions or diagnostic ratios of key product ions can be optimized at specific IR wavelengths. The technique permits both linkage position and anomeric configuration to be assigned. The ratio of the fragments derived by cleavage at the glycosidic bond (m/z 169/187) is much enhanced for beta-anomers compared to alpha-anomers. Differences in the diagnostic product ions 169 and 187 were largest in the range of 9.0-9.4 microm, where the maximum dissociation yield was observed. Conversely, at 10.6 microm, the wavelength of nontunable CO2 lasers that accompany commercial Fourier transform ion cyclotron resonance mass spectrometers, the dissociation yield was poor and anomeric differentiation was not possible. In contrast to previous studies by collision-induced dissociation, the trends in dissociation behavior between anomers using IR-MPD are significant and allow simple diagnostic rules to be established. By depositing energy into these isobaric ions via narrow-band IR excitation, the resulting internal energy can be finely controlled, thereby obtaining high reproducibility in dissociation patterns. Given the multidimensionality of variable-wavelength IR-MPD of lithiated disaccharides, it is expected that this approach can overcome some of the current limitations in isomer differentiation.
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