Manipulation of Electrospray-Produced Biomolecular Ions with Acoustic Fields at Atmospheric Pressure

The coupling of electrospray ionization (ESI) with the newly discovered acoustic ion manipulation (AIM) phenomenon is demonstrated for biopolymeric ions, including peptides, proteins, and oligonucleotides. It is shown that large (i.e., up to ca. 29 kDa) and multiply charged ions are influenced by the presence of acoustic fields. Specifically, we demonstrate the ability to gate, modulate, redirect, and focus these biomolecular ions with an acoustic field. To ensure effective acoustic control of ESI-generated ions, it was necessary to desolvate the electrospray droplets and ions prior to the AIM field through optimization of drying tube temperature and spray gas pressure. In general, small and highly charged ions were more readily deflected from the unstable antinode region toward the acoustic nodes. This trend extended to a charge-state-dependent behavior for protein ions, where higher-charge ions of the same molecule were redirected more easily than their lower-charge counterparts. This work lays a foundation for the implementation of AIM in the study of biomolecules as well as other analytes introduced by ESI to ion-based spectroscopic techniques, such as mass spectrometry and ion mobility spectrometry.