High-resolution field asymmetric waveform ion mobility spectrometry using new planar geometry analyzers

Area of Science:

• Analytical Chemistry
• Separation Science
• Mass Spectrometry

Background:

• Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) is a key technique for gas-phase ion separation, often coupled with Mass Spectrometry (MS).
• Current FAIMS/MS systems predominantly use cylindrical (c-) geometry due to ease of MS coupling.
• A detailed comparison of planar (p-) and cylindrical (c-) FAIMS geometries has been lacking.

Purpose of the Study:

• To theoretically and experimentally compare the performance of planar and cylindrical FAIMS geometries.
• To investigate the impact of FAIMS electrode geometry on ion separation resolution and analysis speed.
• To develop and validate a novel planar FAIMS system for enhanced ion mobility analysis.

Main Methods:

• A priori simulations were performed to evaluate the theoretical resolving power of planar versus cylindrical FAIMS.
• A new planar FAIMS device was constructed, featuring a curtain plate interface for Electrospray Ionization (ESI) and an ion funnel interface with a slit aperture for MS coupling.
• The performance of the new planar FAIMS was experimentally assessed and compared to existing c-FAIMS systems.

Main Results:

• Simulations indicated that reducing FAIMS curvature (i.e., planar geometry) consistently improves resolution at equivalent sensitivity.
• Planar FAIMS demonstrated a resolving power 2-4 times greater than cylindrical FAIMS for various ion species and carrier gases.
• The newly constructed planar FAIMS achieved up to a 4-fold increase in resolution compared to c-FAIMS, with analysis times reduced by approximately half.
• The enhanced planar FAIMS successfully separated challenging species like protonated leucine/isoleucine and bradykinin isomers.

Conclusions:

• Planar FAIMS geometry offers significant advantages in ion separation resolution and analysis speed over cylindrical geometry.
• The developed planar FAIMS system provides a substantial improvement for analyzing complex ion mixtures, enabling the separation of previously unresolved species.
• Further optimization may be needed for analyzing complex systems like protein conformers due to potential multiple unresolved geometries.