Transmitting and Filtering Ions in the Open Air by Applying Spirally Rotating Electric Fields to a Flexible and...

There are many potential advantages to performing ion manipulations at atmospheric pressure (AP) compared to in vacuum. However, the RF electric fields commonly employed in vacuum-based systems are mostly effective at low pressures (<30 Torr), and substitutes for RF generally only perform well over short distances when operated at AP. The study herein describes a new approach for transmitting and filtering ions at AP using spirally rotating electric fields instead of DC or RF voltages. The spirally rotating electric fields were created by (1) splitting traditional ring electrodes into eight identical segments, (2) applying eight 45° phase-shifted waveforms to the segments, and (3) applying waveforms with the same phase to diagonal segments on subsequent electrodes (e.g., seg₁|elec₁ to seg₂|elec₂). Tetraalkylammonium (TAA) and peptide cations were transmitted through a flexible 32 cm length device (5 mm i.d.) operating with 2-7 kHz and 500-1300 V_pp. Ions were detected using a time-of-flight mass spectrometer. Ion signals rose sharply as the frequency was ramped from low to high and gradually decreased after reaching a maximum. Larger ions like TAA-C8 exhibited maximum signals at lower frequencies (e.g., 3.0 kHz, 1000 V_pp), while smaller ions like TAA-C2 exhibited maximum signals at higher frequencies (e.g., 6.5 kHz, 1000 V_pp). These observations demonstrate strong high pass filtering and modest bandpass filtering capabilities at AP. Additionally, ion transmission efficiencies were similar when the flexible device was operated in straight and bent (70°) configurations, showcasing the ability of spirally rotating electric fields to transmit ions through curved geometries. This study establishes the principle of using spirally rotating electric fields to transmit and filter ions at AP and provides a basis for further development of novel AP ion manipulation technologies.