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

Significance of the Topic

The integration of high resolution cyclic ion mobility separation with DESI mass spectrometry imaging addresses critical challenges in spatial metabolomics and lipidomics. DESI enables direct analysis of unmodified tissues, while multi‐pass cyclic IMS distinguishes isobaric and isomeric species, enhancing chemical specificity and imaging peak capacity.

Objectives and Study Overview

The study aimed to implement a scalable multi‐pass cyclic IMS device in DESI imaging to achieve superior separation of small molecules directly on tissues. Key objectives included:

• Optimizing the number of IMS passes to maximize resolution for phospholipid and bile acid isomers.
• Demonstrating separation performance on mouse brain and porcine liver sections.
• Correlating enhanced IMS resolution with confident MS/MS identification and spatial distribution.

Methodology

Tissue sections (mouse brain and porcine liver) were cryosectioned and stored at –80 °C. DESI conditions: 98:2 methanol:water solvent at 2 µL/min, 0.6 kV spray voltage, nitrogen nebulizing gas (10 psi), and 100 µm pixel size. Mass spectra were acquired in positive and negative modes over m/z 50–1,200 on the SELECT SERIES Cyclic IMS. IMS passes ranged from one to thirteen to modulate resolving power. Data processing and image visualization employed MassLynx V4.2, DriftScope V2.9, and HDI 1.6.

Used Instrumentation

• SELECT SERIES Cyclic IMS mass spectrometer
• Desorption electrospray ionization source with high-performance sprayer
• Nitrogen nebulizing gas system
• Cryotome for tissue section preparation
• MassLynx V4.2, DriftScope V2.9, and HDI 1.6 software

Main Results and Discussion

Increasing the number of IMS passes markedly improved separation. Seven passes achieved baseline separation of two phospholipid isobars at m/z 810.6, revealing distinct localization of PC(18:0_20:4) and PC(18:0_18:1) in mouse brain. Thirteen passes resolved bile acid conjugate isomers TDCA and TCDCA (m/z 498.29) in porcine liver with distinct drift times (102.7 ms vs. 103.9 ms). Mobility‐filtered MS/MS confirmed structural assignments and spatial distributions.

Benefits and Practical Applications

High‐resolution cyclic IMS in DESI imaging offers:

• Enhanced peak capacity by resolving overlapping isobaric and isomeric species.
• Improved confidence in MS/MS‐driven structural identification.
• Accurate spatial mapping of metabolites and lipids for biomarker discovery and pathology studies.

Future Trends and Opportunities

Future developments may include dynamic pass count control for optimized throughput, integration with complementary separation and spectroscopic techniques, and advanced data analytics for real‐time tissue profiling. These enhancements will broaden applications in spatial omics and clinical diagnostics.

Conclusion

Multi‐pass cyclic ion mobility integration with DESI imaging significantly enhances the separation of isobaric and isomeric molecules on tissue sections, leading to higher analytical specificity and reliable spatial localization. This approach holds strong potential for advancing spatial metabolomics and lipidomics in biomedical research.

References

No external references were provided in the original text.