HIGH RESOLUTION MULTI-REFLECTING TIME-OF-FLIGHT MASS ANALYZER WITH FOLDED FLIGHT PATH

Importance of High-Resolution TOF Mass Spectrometry

Time-of-flight mass analyzers combine unlimited mass range, rapid spectrum acquisition and minimal spectral distortion, making them highly valuable in applications requiring precise mass assignments. Enhancing resolving power in TOFMS is critical for distinguishing isobaric ions and assigning elemental compositions with confidence in complex matrices.

Objectives and Overview

This work presents the development and implementation of a folded flight path (FFP) multi-reflecting TOF mass analyzer. It aims to extend ion flight time within compact vacuum chambers to achieve high and ultra-high resolving powers (>25 000 and >50 000 at m/z 219) while maintaining practical instrument dimensions and transmission.

Methodology and Instrumentation

• Ion Generation and Acceleration: Ions produced by electron ionization (EI) or multimode sources are transferred into an orthogonal accelerator to form narrow ion packets.
• Folded Flight Path (FFP) Analyzer: Gridless planar electrostatic mirrors and a series of Einzel lens arrays guide ions on a zig-zag trajectory with 32 reflections, yielding ~20 m path length in a < 1 m analyzer volume.
• Vacuum and Detection: Dual turbomolecular pumping stages maintain high vacuum. A fast ion detector and custom digitizer record time-of-flight with nanosecond precision.
• Encoded Frequent Pushing (EFP): Multiplexed pulsing sequences increase duty cycle by >10× through real-time deconvolution of overlapping ion packets.

Main Results and Discussion

• Resolution Performance: In High Resolution (HR) mode, the FFP achieves >25 000 resolving power at m/z 219 (FWHH). In Ultra High Resolution (UHR) mode, the same narrow peak widths over doubled flight times yield >50 000 resolving power.
• Mass Range and Acquisition: HR mode covers the full mass range without truncation. UHR mode reduces acquisition window by factor ~4 (e.g., m/z 100–400) to accommodate double passes.
• Consistent Resolution Trend: Experimental curves show resolution rising at low m/z and plateauing at higher values, a signature advantage of TOFMS over trap-based analyzers.
• Duty Cycle Enhancement: EFP implementation preserves high resolution while boosting usable ion fraction, improving sensitivity.

Benefits and Practical Applications

• Isobar Separation: Distinguishes close-lying ions in environmental, petrochemical and forensic analyses.
• High Throughput: Rapid acquisition complements GC, LC or other front-end separations for complex sample profiling.
• Mass Accuracy: Narrow peaks and stable optics enable confident elemental formula assignment and trace-level quantitation.
• Versatile Coupling: Compatible with multiple ionization sources and separation techniques in QA/QC and research labs.

Future Trends and Potential Uses

• Extending Path Length: Further folding or mirror configurations to push resolution beyond 100 000 in manageable footprints.
• Hybrid Architectures: Combining FFP with ion mobility or high-field asymmetric separations for multidimensional analysis.
• Advanced Duty Cycle Schemes: Refined multiplexing algorithms to approach 100% ion utilization without sacrificing resolving power.
• Portable High-Resolution Systems: Miniaturized FFP designs for field-deployable high-resolution MS.

Conclusion

The folded flight path TOF mass analyzer represents a novel solution for achieving high and ultra-high resolving powers within compact instruments. Its gridless mirror design and spatial focusing lens arrays enable ~20 m flight paths, delivering resolutions up to 50 000 (m/z 219) and enhanced duty cycles via EFP. This technology expands the capabilities of TOFMS in demanding analytical applications requiring both speed and precision.

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