BENEFITS OF HIGH RESOLUTION ION MOBILITY SEPARATION ON THE CYCLIC IMS FOR DESI MASS SPECTROMETRY IMAGING

Significance of the Topic

Desorption Electrospray Ionization (DESI) mass spectrometry imaging enables direct profiling and spatial mapping of metabolites and lipids in unmodified biological tissues. However, distinguishing structurally similar or isobaric species remains challenging. High-resolution ion mobility separation (IMS) addresses this limitation by enhancing peak capacity and specificity, critical for reliable molecular imaging in research and clinical applications.

Objectives and Study Overview

This study evaluated the impact of multi-pass cyclic IMS on DESI-MSI performance. By varying the number of IMS passes, researchers assessed improvements in the separation of isobaric and isomeric compounds and examined their spatial distributions in mouse brain and porcine liver tissue sections.

Methodology and Instrumentation

• Sample Preparation: Cryosectioned mouse brain and porcine liver tissues analyzed without prior chemical modification.
• Ionization: DESI-XS source using methanol/water (98:2) at 2 µL/min flow rate.
• Ion Mobility Separation: SELECT SERIES Cyclic IMS with a traveling-wave device enabling adjustable multi-pass separations.
• Data Processing: Modified Driftscope 2.9, High Definition Imaging (HDI) 1.6, and MassLynx software for mobilogram extraction and image reconstruction.

Key Results and Discussion

• Single-pass IMS produced broad, unresolved peaks (e.g., m/z 810.6 at 24.49 ms) distributed across the tissue section.
• Multiple IMS passes (7 and 13) yielded distinct drift time peaks, successfully separating isomeric lipids and bile acid conjugates such as TDCA (102.69 ms) and TCDA (103.88 ms).
• Higher pass numbers increased overall peak capacity and improved specificity, enabling clearer visualization of structurally similar phospholipids directly in imaging experiments.

Practical Benefits and Application

The cyclic IMS-enhanced DESI-MSI workflow offers:

• Resolution of isobaric and isomeric species, improving molecular specificity.
• Enhanced imaging contrast and quantitative reliability in complex tissue analyses.
• Seamless integration with existing DESI setups, facilitating adoption in metabolomics, lipidomics, and clinical pathology laboratories.

Future Trends and Potential Applications

Emerging developments may include:

• Increased pass capacities for ultra-high resolution separations of complex mixtures.
• Integration with additional ambient ionization techniques to expand analyte coverage.
• Real-time IMS-MS imaging for intraoperative diagnostics and high-throughput drug screening.

Conclusion

Incorporating multi-pass cyclic IMS into DESI-MSI significantly improves analytical performance by expanding peak capacity and resolving challenging isobaric compounds. This approach enhances the accuracy of molecular imaging in tissue analyses and holds promise for diverse applications in analytical chemistry, biomedical research, and diagnostics.