Improving Feature Detection and Putative Identification For Tissue Imaging Applications Using the SELECT SERIES™ Multi‑Reflecting-ToF (MRT) Mass Spectrometer

Significance of the Topic

Mass spectrometry imaging (MSI) of biological tissues plays a vital role in life sciences, pharmaceuticals, and clinical research by enabling spatial mapping of molecular distributions. High mass resolution and accuracy are essential to distinguish closely related compounds and to reliably identify putative biomarkers associated with disease, toxicity, or physiological changes.

Objectives and Study Overview

This study evaluates the performance of the SELECT SERIES MRT multi-reflecting‐ToF mass spectrometer for desorption electrospray ionization (DESI) imaging of murine adrenal gland tissue, comparing its mass resolution and accuracy against a conventional oa-QToF instrument. The aim is to demonstrate improved feature detection, fine isotope resolution, and confidence in elemental composition assignments.

Methodology and Instrumentation

Cryo-sectioned wild-type mouse adrenal glands (15 µm thickness) were analyzed by DESI-MSI in both positive and negative modes at 25 µm pixel resolution.

• SELECT SERIES MRT Mass Spectrometer: employs two gridless electrostatic mirrors for multiple ion reflections, extending flight path to >48 m; mass resolution >200,000 FWHM; mass accuracy <500 ppb.
• Conventional oa-QToF Mass Spectrometer: standard research-grade instrument with ~20,000 FWHM resolution.
• Software workflows: MassLynx for spectrum evaluation and elemental composition; HDI for image generation and peak lists; LIPID MAPS database for putative identifications; MetaboAnalyst for statistical analysis.

Main Results and Discussion

The MRT instrument revealed fine isotope patterns and separated signals that appeared as a single unresolved peak on the oa-QToF. A complex feature at nominal m/z 806.55 was resolved into three distinct peaks (m/z 806.51007, 806.55829, 806.56909) with unique localizations in the cortex and medulla regions.

• Positive mode putative lipids: LPC 16:0/LPE 19:0, PC 38:4/PE 41:4, cholesterol fragment.
• Negative mode putative lipids: LPE 20:4, PI 39:4, LPC 13:0.
• MRT accuracy (<500 ppb) reduced the number of candidate elemental compositions, boosting confidence in identifications.

Benefits and Practical Applications

• Enhanced detection of low‐abundance and isobaric species.
• Improved spatial differentiation of biomarkers within tissue microanatomy.
• Streamlined identification workflows with higher confidence in database searches.
• Compatibility with existing MS imaging software and statistical tools.

Future Trends and Opportunities

Anticipated developments include integration with multimodal imaging techniques, high-throughput tissue analyses, AI-driven data interpretation, and translation to clinical diagnostics. Ongoing improvements in instrument speed and data processing will further expand MSI applications in biomedical research.

Conclusion

The SELECT SERIES MRT mass spectrometer significantly enhances feature detection and putative identification in DESI-MSI of tissue specimens. Its superior resolution and accuracy uncover detailed isotope structure, reduce ambiguities in elemental composition, and facilitate confident biomarker discovery in complex biological samples.

References

1. US Department of Health and Human Services, NIH. Adrenal Gland Disorders.
2. Pang Z., Zhou G., Ewald J. et al. Using MetaboAnalyst 5.0 for LC–HRMS spectra processing, multi‐omics integration and covariate adjustment of global metabolomics data. Nat Protoc (2022).
3. Fahy E., Subramaniam S., Murphy R. et al. Update of the LIPID MAPS comprehensive classification system for lipids. Journal of Lipid Research 50, S9–S14 (2009).