Speaker
Description
Electrospray ionization (ESI) is the most widely used ionization technique in liquid chromatography-mass spectrometry (LC-MS), generating charged microdroplets that undergo evaporation and Coulomb fission to produce gas-phase ions. However, in high-flow ESI regimes, a significant fraction of large, highly charged droplets (up to 100μm) can enter the MS inlet. These droplets contribute to contamination of ion optics, increased chemical noise, and degradation of detector performance. In this work, we introduce a new approach for active control of ESI-generated aerosols, enabling steering of the aerosol stream using acoustic radiation forces induced by airborne ultrasound. Acoustic fields are generated by a phased array of 240 ultrasonic emitters operating at 40 kHz, with independent amplitude and phase control. This enables dynamic shaping of the acoustic field, allowing the formation of pressure distributions such as extended focal regions and acoustic vortices between the ESI source and the MS inlet. The ultrasonic system is integrated with a Bruker amaZon ETD quadrupole ion trap mass spectrometer, allowing direct assessment of the influence of the acoustic field on mass spectral signals. Aerosol imaging experiments demonstrate controlled steering of ESI aerosol flows under acoustic excitation. The application of ultrasound altered the measured mass spectra, shifting components with high m/z values toward lower values. We further investigate the underlying mechanisms of acoustic–aerosol interactions using various mass spectrometer operating modes and evaluate the impact of ultrasonic field configurations on analyte transmission and mass spectral measurements. This approach demonstrates a contactless, reconfigurable method for aerosol control in LC–MS, opening new possibilities for improving measurement stability and reducing device contamination.