Single-Photon-Induced Post-Ionization to Boost Ion Yields in MALDI Mass Spectrometry Imaging

摘要

Matrix-assisted laser desorption/ionization mass spectrometry imaging(MALDI-MSI)is a rapidly growing method in the life sciences.However,for many analyte classes,its sensitivity is limited due to poor ionization efficiencies.To mitigate this problem,we here introduce a novel post-ionization scheme based on single-photon induced chemical ionization using pulsed RF-Kr lamps.The fine-vacuum conditions of a dual ion-funnel ion source effectively thermalize the evolving MALDI plume and enable ample gas-phase reactions.Injected chemical dopants crucially support fragment-less ionization to[M+H]~+/[M-H]~-species.Based on this interplay,numerous glycerophospho-,sphingo-,and further lipids,registered from mammalian tissue sections,were boosted by up to three orders of magnitude,similar to results obtained with laser-based post-ionization(MALDI-2).Experiments with deuterated matrix and dopant,however,indicated complex chemical ionization pathways different from MALDI-2.