Ambient molecular imaging by laser ablation electrospray ionization mass spectrometry with ion mobility separation

Mass spectrometry imaging (MSI) by laser ablation electrospray ionization (LAESI) enables the lateral mapping of molecular distributions in untreated biological tissues. However, direct sampling and ionization by LAESI-MSI limits the differentiation of isobaric ions (e.g., structural isomers) in a complex sample. Ion mobility separation (IMS) of LAESI-generated species is sufficiently fast to be integrated with the MSI experiments. Here, we present an imaging technique based on a novel combination of LAESI-MSI with IMS that enables in vivo and in situ imaging with enhanced coverage for small metabolites. Ionized molecules produced at each pixel on the tissue were separated by a traveling wave IMS and analyzed by a high performance quadrupole time-of-flight mass spectrometer. Plant (Pelargonium peltatum leaves) and animal tissues (frozen mouse brain sections) were imaged under atmospheric pressure. In LAESI-IMS-MSI, a multidimensional dataset of m/z, drift time (DT), ion intensity, and spatial coordinates was collected. Molecular images for the P. peltatum leaf illustrated that the distributions of flavonoid glycoside ions are aligned with a vein pattern in the tissue. Differentiation of isobaric ions over DT reduced the chemical interferences and allowed separate imaging of these ions. Molecular images were constructed for selected ions in the sagittal sections of the mouse brain, and isobaric species were distinguished by differences in drift times corresponding to distinct molecular structures or conformations. We demonstrated that IMS enhanced the metabolite coverage of LAESI in biological tissues and provided new perspective on MSI for isobaric species. (C) 2014 Elsevier B.V. All rights reserved.