Overview

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Webinar Summary

In this webinar, we discuss research that shows increased molecular coverage of metabolites and drugs by utilizing both MALDI and DESI. The imaging experiments were performed on a quadrupole time-of-flight mass spectrometer equipped with swappable MALDI and DESI ion source (SYNAPT HDMS G2-Si or Xevo G2-XS; Waters Corporation, Milford, MA), and the data were collected and analyzed using High Definition Imaging (HDI) software. Molecular assignments were obtained from the accurate mass search against publicly curated databases to gauge preferential ionization of specific molecule classes. Statistical analysis of ions detected by DESI and MALDI on consecutive sections of tissue alluded to the complementary characteristics of the two mechanistically different ionization sources. We will examine how enhanced molecular coverage was obtained by combining data from the two techniques, painting a more comprehensive molecular picture.

In the last decade, both matrix-assisted laser desorption/ionization (MALDI) and desorption electrospray ionization (DESI) mass spectrometry (MS) imaging have been developed to image smaller molecules, such as metabolites and lipids, from the tissue. DESI often detects a complementary set of molecules to MALDI due to preferential ionization of those species by electrospray. For instance, DESI readily detects neurotransmitters, such as serotonin, adenosine, and glutamine directly from mouse brain tissue samples, while MALDI can readily visualize molecules such as ATP, ADP, AMP, UDP. The complementary nature of these two ionization techniques is also found in the analysis of pharmaceutical drug molecules in the biological matrix.

Key Learning Objectives

• Learn how increased molecular coverage of metabolites and drugs was achieved by utilizing both modalities of MS imaging
• Understand how the spatial distribution of a molecular species can provide a wealth of information
• See how DESI uses an ambient ionization technique that can achieve high spatial resolution MS imaging with little to no sample preparation
• Understand the benefits of using complementary technologies in cases where MALDI mass spectrum suffers from the presence of matrix clusters