Single‐Photon‐Induced Post‐Ionization to Boost Ion Yields in MALDI Mass Spectrometry Imaging. Issue 34 (14th July 2022)

• Record Type: Journal Article
• Authors: Bookmeyer, Christoph; Röhling, Ulrich; Dreisewerd, Klaus; Soltwisch, Jens
• Is Part Of: Angewandte Chemie international edition. Volume 61:Issue 34(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-07-14
• Subjects: Analytical Methods -- Lipidomics -- MALDI-MS Imaging -- Mass Spectrometry -- Post-Ionization; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202202165
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: 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. Abstract : A new efficient post‐ionization strategy for MALDI‐MS imaging is presented: Simple RF‐Kr lamps were pulsed and synchronized with a MALDI laser using custom‐made electronics. Initial photoionization of dopant vapor in the fine‐vacuum ion‐funnel source yielded >100× signal boosts of numerous lipid classes from mammal tissue sections. Deuterated components indicated complex gas‐phase ionization pathways generating fragment‐less [ M +H] + /[ M −H] − species.