Lecture
Acoustic Ion Manipulation (AIM) to Control, Focus, and Separate Biomolecular Ions at Atmospheric Pressure
- at -
- ICM Saal 5
- Type: Lecture
Lecture description
J.T. Shelley, Troy/US, J.L. Danischewski, Troy/US, Y. You, Berlin/DE, J. Hufgard, Berlin/DE, J. Riedel, Berlin/DE
Approaches to control the motion and direction of ionized atoms and molecules are an essential aspect of ion-based analytical methods, such as mass spectrometry (MS) and ion-mobility spectrometry (IMS). Because these species are charged, most ionmanipulation approaches rely upon electrostatic and/or Lorentz forces in electric and magnetic fields, respectively. The ability to produce intact gaseous ions for MS and IMS is often performed at atmospheric pressure (AP) due to ease of sample introduction, high ionization efficiencies, and minimal fragmentation. However, at AP, diffusion and the small mean free path require higher field strengths and electrodes in the beam path (e.g., wires or grids) to overcome the dominating aerodynamic effects. These issues are especially pronounced for large biopolymers, which can only be ionized at AP.
Here, we describe and explore a phenomenon whereby low-power acoustic fields are used to move, shape, gate, and separate beams of gaseous ions at atmospheric pressure. We refer to this approach as Acoustic Ion Manipulation (AIM). The initial demonstration of AIM at AP was with small ions generated by electrical plasmas (e.g., H₃O⁺, N₂⁺ , etc.). These ions were directed towards, and separated by, the presence of time varying pressure gradients. To better understand the phenomenon, an ion-detector array provided a measure of bulk ion movement, while mass spectrometry (MS) offered mass- and charge-dependent information. As one example of an AIM setup, a standing
acoustic wave was formed with two ultrasonic speakers and placed between an ionization source and a detector. Ion beams were deflected away from unstable pressure regions (i.e. antinodes) into the pressure-stable nodal areas. Shadowgraphy revealed that the neutral gas stream continued through an antinode and, thus, ions were separated from the transport gas. Interestingly, both positive and negative ions follow this same trajectory indicating that charge, but not polarity, is a driving factor in AIM.
More recently, we have successfully interfaced AIM with electrospray ionization (ESI) for the control of large, highly charged biomolecular ions (e.g., peptides, proteins, and oligonucleotides). Coupling AIM with ESI has revealed a charge-state dependence in the phenomenon where highly charged ions are more greatly influenced by the acoustic field.
Specific examples of focusing, gating, and separation with AIM will be shown. This work demonstrates the basis for a simple, inexpensive ion-optic tool that is easily constructed with low-power, off-the-shelf components.
Approaches to control the motion and direction of ionized atoms and molecules are an essential aspect of ion-based analytical methods, such as mass spectrometry (MS) and ion-mobility spectrometry (IMS). Because these species are charged, most ionmanipulation approaches rely upon electrostatic and/or Lorentz forces in electric and magnetic fields, respectively. The ability to produce intact gaseous ions for MS and IMS is often performed at atmospheric pressure (AP) due to ease of sample introduction, high ionization efficiencies, and minimal fragmentation. However, at AP, diffusion and the small mean free path require higher field strengths and electrodes in the beam path (e.g., wires or grids) to overcome the dominating aerodynamic effects. These issues are especially pronounced for large biopolymers, which can only be ionized at AP.
Here, we describe and explore a phenomenon whereby low-power acoustic fields are used to move, shape, gate, and separate beams of gaseous ions at atmospheric pressure. We refer to this approach as Acoustic Ion Manipulation (AIM). The initial demonstration of AIM at AP was with small ions generated by electrical plasmas (e.g., H₃O⁺, N₂⁺ , etc.). These ions were directed towards, and separated by, the presence of time varying pressure gradients. To better understand the phenomenon, an ion-detector array provided a measure of bulk ion movement, while mass spectrometry (MS) offered mass- and charge-dependent information. As one example of an AIM setup, a standing
acoustic wave was formed with two ultrasonic speakers and placed between an ionization source and a detector. Ion beams were deflected away from unstable pressure regions (i.e. antinodes) into the pressure-stable nodal areas. Shadowgraphy revealed that the neutral gas stream continued through an antinode and, thus, ions were separated from the transport gas. Interestingly, both positive and negative ions follow this same trajectory indicating that charge, but not polarity, is a driving factor in AIM.
More recently, we have successfully interfaced AIM with electrospray ionization (ESI) for the control of large, highly charged biomolecular ions (e.g., peptides, proteins, and oligonucleotides). Coupling AIM with ESI has revealed a charge-state dependence in the phenomenon where highly charged ions are more greatly influenced by the acoustic field.
Specific examples of focusing, gating, and separation with AIM will be shown. This work demonstrates the basis for a simple, inexpensive ion-optic tool that is easily constructed with low-power, off-the-shelf components.
