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Nanospray Desorption Electrospray Ionization (nano-DESI) Mass Spectrometry Imaging of Drift Time-Separated Ions

Simultaneous spatial localization and structural characterization of
molecules in complex biological samples currently represents an analytical
challenge for mass spectrometry imaging (MSI) techniques. In this study, we
describe a novel experimental platform, which substantially expands the
capabilities and enhances the depth of chemical information obtained in high
spatial resolution MSI experiments performed using nanospray desorption
electrospray ionization (nano-DESI). Specifically, we designed and constructed
a portable nano-DESI MSI platform and coupled it with a drift tube ion mobility
spectrometer-mass spectrometer (IM-MS). Separation of biomolecules observed in
MSI experiments based on their drift times provides unique molecular
descriptors necessary for their identification by comparison with databases. Furthermore,
it enables isomer-specific imaging, which is particularly important for
unraveling the complexity of biological systems. Imaging of day 4 pregnant
mouse uterine sections using the newly developed nano-DESI-IM-MSI system demonstrates
 rapid isobaric and isomeric separation
and reduced chemical noise in MSI experiments. A direct comparison of the
performance of the new nano-DESI-MSI platform operated in the MS mode with the
more established nano-DESI-Orbitrap platform indicates a comparable performance
of these two systems. A spatial resolution of better than ~16 µm and similar molecular
coverage was obtained using both platforms. 
The structural information provided by the ion mobility separation
expands the molecular specificity of high-resolution MSI necessary for the
detailed understanding of biological systems.