Differentiation of isomers by wavelength-tunable infrared multiple-photon dissociation-mass spectrometry: application to glucose-containing disaccharides.

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.