

Aerospace Laboratory for Plasma Experiments
Novel Miniature Coaxial
Ion Trap Mass Spectrometer
The Simplified Coaxial Ion Trap (SCIT) project, in collaboration with the Department of Chemistry and Biochemistry at Brigham Young University, aims to develop and characterize a miniaturized mass spectrometry device for portable chemical analysis. This project integrates three established ion traps — the Simplified Toroidal Ion Trap (STorIT), the Rectilinear Ion Guide (RIG), and the Cylindrical Ion Trap (CIT) — into a single device. The goal is to create a versatile analytical platform to efficiently store many ions for selective tandem mass analysis.
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System Process:
Gases from helium bottles and glass vials of samples flow through their respective feed lines into the manifold (illustrated on the right). The various SCIT electrodes are energized with either direct current (DC) potentials or radio frequency (RF) signals around one megahertz.
Next, a thermionic electron gun emits a spray of electrons collimated and gated by an einzel lens, referred to as the "E-Gun Gate" (also shown in the right image). This collimated beam of electrons enters the RIG, where the gases are mixed. Due to electron impact ionization, the sample gases become charged as electrons are stripped away by the electron beam. Additionally, due to this ionization method's "hard" nature, molecules tend to break apart into fragment ions. This fact is a surprise tool that will help us later.
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Rendered CAD images of the partially constructed SCIT, with components labeled. The red and blue spheres represent trapped ions.
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With inert helium gas that slows fast-moving ions and high-amplitude RF fields that actively stabilize the position of the ions, the sample ions are trapped within a "trapping potential well" along the central axis of the STorIT and RIG (depicted by the line of red and blue spheres above). As the ions move within the trapping region at a secular frequency, an alternating current (AC) is applied through the "AC Electrode". This signal resonates with the ions' secular frequency, allowing kinetic energy to grow until the ions leave the STorIT to the CIT through the gap between the electrodes. Ions with sufficiently moderate kinetic energy become trapped within the CIT, successfully transferring them from one ion trap to another. Ions with too little energy return to the STorIT, and ions with too much energy fly through the CIT, terminating elsewhere.
Using the same process of harmonious resonant ejection, the ions can be ejected from the CIT to a detection setup (not shown). Currently, this system employs a conversion dynode and electron multiplier tube pair. Ions that impact the conversion dynode cause secondary electron emission. These electrons then travel through a large potential difference to the electron multiplier tube, which amplifies the electrons into an electric current that an oscilloscope can detect.
Since this process occurs over a few hundred milliseconds and ions are selectively ejected by mass sequentially over time, the result is a desired mass spectrum.
Project Goals:
As mentioned earlier, the three ion trap geometries are well established in the literature. Which raises the question: If these ion traps have been previously demonstrated, why combine them? Each geometry has its advantages and disadvantages, and when integrated, they can offer greater value than their contributions.
The RIG and the STorIT provide larger ion storage capacities than the CIT's specific point storage, though they sacrifice some mass resolution. The CIT takes advantage of the central void in a toroidal ion trap, where there are typically no electrodes. In previous studies developing precursor devices, the central axis of a Toroidal Ion Trap (TorIT) is used to house the detection equipment; however, in this new configuration, the CIT occupies that central space, and the detection hardware is placed elsewhere.
When these three geometries are combined, they enable "tandem" mass analysis, allowing for various simultaneous analyses. The RIG provides a long, straight axis for the electron beam, which ionizes sample gases along its length. The STorIT, as its acronym suggests, stores sample ions and selectively transfers them into the CIT. When a targeted mass is isolated in the CIT from the bulk sample, a mass analysis process called "collisionally induced dissociation" occurs. In this process, the target ion is fragmented as it collides with itself and the surrounding buffer gas, producing fragment ions that create a unique molecular fingerprint. This fingerprint can be used to identify the parent target ion further.
Combining a high-storage ion trap with a high-resolution tandem mass analyzer has significant implications for the miniaturization of ion trap-based mass analyzers. As the size of the devices decreases, the quantity of ions that can be stored also shrinks. The combined geometry of the SCIT can help overcome the challenges associated with miniaturization, paving the way for portable ion traps. With portable mass analyzers, we can envision various applications that could benefit from in situ mass analysis, such as uncrewed submarines, aircraft, or spacecraft, field drug analysis by police officers, continuous monitoring of pollutants, and tracer compounds for detecting leaks in oilfields.
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Results
Previous research has examined a partially constructed SCIT, in which the CIT's end cap electrodes have been removed to evaluate the combined STorIT and RIG sections' storage and ejection capabilities.
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Objectives of STorIT Characterization:
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Evaluate the ion trapping capacity of the STorIT component under varying ionization conditions.
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Quantify ion storage efficiency and identify ion loss mechanisms within the toroidal trapping region.
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Determine mass spectral resolution across different ion populations.
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Characterize the efficiency and selectivity of resonance-based mass ejection from the STorIT into the central CIT.
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Establish operational parameters necessary for the future assembly and testing of the complete SCIT device.
STorIT Characterization:
Experiments have demonstrated that the STorIT component can effectively trap over 250,000 ions without compromising performance. At low to moderate ion loads, the mass resolution of xenon spectra remains excellent, only worsening at the highest ion counts.
Ion storage experiments revealed a decrease in ions over time, typically within about half a second. This decline primarily occurs due to instabilities at the intersection of the RIG and STorIT. While some minor secondary charge-exchange losses were observed, they are not significant.
Resonance ejection experiments with hydrocarbon compounds (shown right), such as toluene, deuterated toluene, and ortho-xylene, yielded nearly perfect mass ejection efficiencies. At higher ejection voltages, broader selectivity windows were observed. These findings establish necessary performance standards and inform the design of the fully integrated SCIT mass analyzer.
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Examples of mass spectra collected using STorIT for various hydrocarbons.
Fully Assembled SCIT Characterization:
The team at ALPE is currently in the process of characterizing the fully assembled SCIT. Unlike the research detailed in the previous section, the SCIT is now completely constructed. In past research, the CIT had one of its end caps removed, which allowed for the near-instantaneous ejection of ions rather than their transfer and capture by the CIT. Now that the CIT is fully assembled with both end caps intact, it can transfer and capture ions effectively.
After confirming that the two ion traps can operate in tandem without any electrical discharging issues, the team will work to demonstrate tandem mass analysis. By utilizing various fluorinated molecules, such as sulfur hexafluoride and perfluoromethylcyclopentane, which have distinct molecular fingerprints, the team can verify the mass spectra of these molecules, isolate one of their prominent ions, and conduct CID analysis (MS²) as illustrated in the figure below.
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Examples of mass spectra illustrating the tandem mass analysis process using fluorinated compounds (specifically, Sulfur Hexafluoride and [Perfluoro]methylcyclopentane): a) A mass spectrum of the molecule obtained through electron impact ionization. b) A mass spectrum demonstrating the isolation bandwidth around a target ion as it moves from the STorIT to the CIT. c) A mass spectrum resulting from collisionally induced dissociation.
Next Steps:
Future work will focus on fully realizing the device by establishing the necessary processes, including troubleshooting the capacitive effects resulting from the electrodes operating in proximity, demonstrating in situ analysis by obtaining the mass spectra of pollutants in lab air, and enabling the analysis of hazardous drug substances using alternative paper spray ionization methods.
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Finally, based on the project's results, a portable, handheld device utilizing a simplified coaxial ion trap will be developed.
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Funding Sources:
This work was funded by the U.S. National Science Foundation (NSF awards 2003667 and 2003592).
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Related literature:​
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Sirbescu-Stanley, D. V., Lemmer, K. M., Austin, D. E., & Taylor, N. R. (2024). A simplified coaxial ion trap mass analyzer: Characterization of the simplified toroidal ion trap with a rectilinear Ion Guide. International Journal of Mass Spectrometry, 506, 117353. https://doi.org/10.1016/j.ijms.2024.117353
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Sirbescu-Stanley, David Virgil, "Diagnosing Discharge Events within a Novel Miniature Simplified Coaxial Ion Trap Mass Analyzer" (2024). Masters Theses. 5414.
https://scholarworks.wmich.edu/masters_theses/5414
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Gamage, Hettikankanange, P. M., Lyman, K. D., Austin, D. E., & Taylor, N. R. (2022). Simplified coaxial ion trap: Simulation-based geometry optimization, unidirectional ejection, and trapping conditions. International Journal of Mass Spectrometry, 474, 116801. https://doi.org/10.1016/j.ijms.2022.116801
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Lyman, K. D. (2022). Design, Manufacture, and Characterization of a Novel Miniature Coaxial Ion Trap Mass Analyzer. Masters Theses. 5353. https://scholarworks.wmich.edu/masters_theses/5353