IRMPD Spectroscopic Analysis of Peptides and Oligosaccharides Using FTICR With Mid-Infrared Free-Electron Laser

The fragmentation in gas-phase peptides and oligosaccharides has been investigated by using electrospray ionization (ESI) Fourier-Transform Ion Cyclotron Resonance (FTICR) mass spectrometry (MS) with a laser cleavage infrared multiphoton dissociation (IRMPD) technique. In order to cleave the ionized sample introduced in the FTICR cell, an infrared free electron laser (FEL) is used for the technique of IRMPD as a tunable infrared light source. The gas-phase infrared spectra of protonated peptides (Angiotensin II, Substance P) and sodiated ologosaccharide (Sialyl Lewis X) are obtained in the range from 5.7 $\mu $m to 9.5 $\mu $m. The results of the IRMPD spectra of the peptides show that the peaks for the photoproducts are observed as y/b type fragment ions in the IR range from 5.7 $\mu $m to 7.5 $\mu $m, corresponding to the cleavage of backbone in the parent amino acid sequence, while the spectra of the oligosaccharide have the peaks for the B/Y type in the range from 7.1 $\mu $m to 9.3 $\mu $m.