Dynamic Range Expansion by Gas-Phase Ion Fractionation and Enrichment for Imaging Mass Spectrometry

Abstract

In the analysis of biological tissue by imaging mass spectrometry (IMS), the limit of detection and dynamic range are of paramount importance in obtaining experimental results that provide insight into underlying biological processes. Many important biomolecules are present in the tissue milieu in low concentrations and in complex mixtures with other compounds of widely ranging abundances, challenging the limits of analytical technologies. In many IMS experiments, the ion signal can be dominated by a few highly abundant ion species. On trap-based instrument platforms that accumulate ions prior to mass analysis, these high abundance ions can diminish the detection and dynamic range of lower abundance ions. Herein, we characterize two strategies for combating these challenges during IMS experiments on a hybrid QqFT-ICR MS. In one iteration, the mass resolving capabilities of a quadrupole mass filter are used to selectively enrich for ions of interest via a technique previously termed continuous accumulation of selected ions (CASI). Secondly, we have introduced a supplemental dipolar AC waveform to the quadrupole mass filter of a commercial QqFT-ICR mass spectrometer to perform selected ion ejection prior to the ion accumulation region. This setup allows the selective ejection of the most abundant ion species prior to ion accumulation, thereby greatly improving the molecular depth with which IMS can probe tissue samples.

Multimodal Imaging Based on Vibrational Spectroscopies and Mass Spectrometry Imaging Applied to Biological Tissue: A Multiscale and Multiomics Review

“…This allows molecules to be detected more readily than they would be without such modifications by adding a readily ionizable functional group . In a different approach, Prentice et al characterized the FT-ICR method of continuous accumulation of selected ions (CASI) and demonstrated selected ion ejection using a quadrupole mass filter with MALDI-MSI . These techniques have improved MALDI-MSI by addressing sensitivity and dynamic range.…”

Clostridioides difficile infection induces a rapid influx of bile acids into the gut during colonization of the host

“…The advent of powerful molecular imaging technologies allows for the visualization of host-microbe interactions within tissue microenvironments ( Cassat et al, 2018 ; Knippel et al, 2018 ; Zackular et al, 2016 ). In particular, recent advances in imaging mass spectrometry (IMS) provide improved sensitivity, specificity, and spatial resolution, presenting a unique opportunity to illuminate these processes in situ and improve our understanding of enteric disease progression along the entire length of the intestinal tract ( Buchberger et al, 2018 ; Niehaus et al, 2019 ; Prentice et al, 2020 ; Spraggins et al, 2019 ; Stoeckli et al, 1999 ).…”

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

“…Many instrumental technologies can be employed for improving sensitivity for IMS experiments. [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.…”