Feasibility of higher-order differential ion mobility separations using new asymmetric waveforms

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Spectrometry

Background:

• Ion mobility spectrometry (IMS) and field asymmetric waveform IMS (FAIMS) have been established for decades for ion separation based on transport properties.
• These techniques, coupled with soft ionization and mass spectrometry (MS), have broadened applications in fields like biomedical research and nanomaterials.
• Current methods primarily rely on absolute mobility (IMS) or mobility differences at high/low fields (FAIMS).

Purpose of the Study:

• To explore the theoretical potential of using time-dependent electric fields with more than two intensity levels for ion separation.
• To demonstrate that higher-order electric fields can achieve distinct differential separations based on higher-order ion mobility terms.
• To assess the practicality and orthogonality of these novel separation methods compared to existing techniques.

Main Methods:

• Theoretical analysis of ion mobility in time-dependent electric fields with multiple intensity levels.
• Extension of conventional IMS (1st order) and FAIMS (2nd order) principles to higher-order separations (4th-5th order and beyond).
• Consideration of hardware and operational similarities to existing FAIMS instrumentation.

Main Results:

• Time-dependent electric fields with >2 intensity levels can theoretically achieve an infinite number of distinct differential separations.
• Higher-order separation methods (up to 4th/5th order) are predicted to be feasible at ambient air field intensities.
• Higher orders are potentially achievable in insulating gases, and available data suggest orthogonality to existing methods (IMS, FAIMS, MS).

Conclusions:

• Advanced electric field waveforms offer a pathway to significantly enhanced ion separation capabilities.
• These higher-order mobility analyses present a novel dimension for ion characterization, orthogonal to current techniques.
• The proposed methods hold promise for expanding the analytical utility of ion spectrometry in complex sample analysis.