MALDI-2 on a Trapped Ion Mobility Quadrupole Time-of-Flight Instrument for Rapid Mass Spectrometry Imaging and Ion Mobility Separation of Complex Lipid Profiles

Abstract

Matrix-assisted laser desorption/ionization combined with laser-induced postionization (MALDI-2) is a recently introduced method for enhanced mass spectrometry imaging of numerous classes of biomolecules, including phospho- and glycolipids in tissue sections at high lateral resolution. Here we describe the first adaptation of the technology to a Bruker timsTOF fleX mass spectrometer. Upon use of a 1 kHz postionization laser, MALDI-2 produces a sizable increase in the number of detected features as well as in ion signal intensities. This enhancement is similar to that described previously for low repetition rate MALDI-2 systems, but now enables substantially enhanced measurement speeds. In our proof-of-concept study, we furthermore demonstrate, on examples of rat brain and testis tissue sections, that the combination of MALDI-2 with the trapped ion mobility spectrometry (TIMS) functionality of the instrument can crucially support unravelling the complex molecular composition of the lipidome. Numerous isomeric/isobaric ion species are successfully separated upon using the collisional cross section (CCS) as additional specific physical property. With the possibilities of high data acquisition speed or high separation powers in combination with the increased sensitivity of MALDI-2 available in one instrument, the described methodology could be a valuable tool in many areas of biological and medical research.

Molecular insights into symbiosis—mapping sterols in a marine flatworm-algae-system using high spatial resolution MALDI-2-MS imaging with ion mobility separation

“…MALDI-2-MSI MSI data were acquired on a modified timsTOF fleX instrument (Bruker Daltonik, Bremen, Germany) [45]. The mass resolving power of this hybrid QTOF-type instrument is about 40,000 (fwhm) in the investigated m/z range of 300-1000 and the mobility resolution is about 200.…”

“…Mobility separation of isobaric compounds thereby significantly aids with tentative assignment of molecular identities (see ESM Fig. S3 for exemplary mobilograms) [45].…”

“…With IMS, ions are separated based on their collisional cross section in a bath gas prior to MS analysis. This allows for the individual analysis of ion species that are isobaric in the m/z domain [45]. Resulting three-dimensional data is usually presented in the form of mobilograms, where m/z information is commonly plotted on the abscissa, mobility separation is commonly plotted on the ordinate, and ion signal intensity is vizualized by a color scale.…”

“…These boundary conditions necessitate both a particular sensitive MS analysis with high chemical depth and simultaneously a high spatial resolution with a pixel size of 5 μm. Next to an increased sensitivity gained by the use of MALDI-2, trapped ion mobility spectrometry (TIMS) is used to increase confidence in the assignment of sterol-derived ion signals on a MALDI-2 timsTOF flex instrument [45].…”

Enhancement of Tryptic Peptide Signals from Tissue Sections using MALDI IMS Post-ionization (MALDI-2)

“…[35][36][37][38][39] One technology that has been shown to dramatically increase signal for MALDI IMS for some analytes is laser-based post-ionization. [40][41][42][43][44][45] This approach ionizes some of the abundant neutrals that are generated during the initial MALDI event. Post-ionization by MALDI-2 employs a secondary laser positioned parallel to, and above the sample to irradiate the plume generated by the initial MALDI event thereby increasing the fraction of molecules that are ionized.…”