Gating Modes in Ion Mobility-Mass Spectrometry: Principles, Advances, and Coupling With Mass Analyzers

Ion mobility-mass spectrometry (IM-MS) provides an additional gas-phase separation dimension and complementary structural and conformational information through collision cross-section (CCS) values. Its analytical performance depends not only on mobility resolving power but also on temporal coordination among ion generation, mobility separation, ion transfer, and mass spectrometric acquisition.

This review examines the principles and recent developments of serial gating modes, including single-gate pulsed injection and dual-gate operation, and multiplexed gating modes, including sequence-encoded, correlation-based, and Fourier transform approaches. These modes are compared in terms of gate duty cycle, ion utilization efficiency, mobility resolving power, sensitivity, acquisition efficiency, reconstruction reliability, and compatibility with mass analyzers having different acquisition timescales.

The comparison shows that serial gating provides direct acquisition and well-defined timing relationships, whereas its ion utilization depends strongly on upstream accumulation and the sampling strategy. Multiplexed gating generally increases the gate-open fraction and admits a larger fraction of the ion beam but requires reliable reconstruction. High-resolution demultiplexing can increase the effective mobility resolving power of sequence-encoded data. Temporal matching requirements differ between fast, continuously acquiring mass analyzers and analyzers with longer or temporally selective acquisition cycles.

Gate duty cycle and ion utilization efficiency are related but distinct performance metrics, and no single gating mode is optimal for all IM-MS platforms. Gating strategies should therefore be selected and optimized according to the analytical objective, ion availability, required mobility resolving power, mass-analyzer acquisition timescale, and tolerance for reconstruction artefacts.