Development of High Pressure Mass Spectrometry for Handheld Instruments

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  • March 19, 2019
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  • Blakeman, Kenion
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • This work describes the development of microscale ion traps intended for high pressure mass spectrometry in handheld mass spectrometers. By operating at pressures approaching 1 Torr, the major size, weight and power (SWaP) contributor, the turbopump can be eliminated. Unlike other mass analyzers, ion traps can successfully operate at higher pressures by reducing the trap size and operating at higher RF drive frequencies. HPMS was first demonstrated with helium buffer gas with volatile organic compounds (VOCs) and a ro = 500 µm cylindrical ion trap (CIT). RF frequencies up to 10 MHz minimized mass resolution loss with pressure. HPMS with nitrogen and air were then explored as field available buffer gases to eliminate helium tanks in the field, reducing instrument size and weight. Peak widths at 1.0 Torr were 0.7 Da for helium and 5 Da for nitrogen and air were observed at RF drive frequencies of 10 MHz. As peak widths widen at high pressures due to more frequent collisions, the RF frequency was increased along with a reduction in trap size to regain mass resolution. Five CITs were operated at 1 Torr in air with RF drive frequencies between 6.14 MHz to 59.44 MHz resulting in peak widths improving from 5.5 Da to 0.8 Da. Stretched length ion traps (SLITs) and 7-element CIT arrays improved sensitivity over the single element traps by factors of 6 and 7. Operating at ambient air pressures between 250 mTorr and 1.0 Torr with RF frequencies between 30 MHz and 60 MHz reduced peak widths to sub-0.6 Da. Finally, printed circuit board (PCB) and silicon ion traps were developed as alternative materials to metal ion traps. Both PCB and Si traps lower trap capacitance reducing RF power needs and improving instrument SWaP. PCB traps had a factor of two lower sensitivity and peak widths within 10% of metal traps while silicon ion traps had twice the signal intensity of metal traps and better peak widths by up to 30 %. In terms of fabrication, PCB traps can be mass produced while Si traps can be produced with higher dimensional fidelity than metal ion traps.
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Rights statement
  • In Copyright
Advisor
  • Ramsey, J. Michael
  • Jorgenson, James
  • Brustad, Eric
  • Cahoon, James
  • Lockett, Matthew
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2015
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  • Chapel Hill, NC
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  • There are no restrictions to this item.
Date uploaded
  • August 25, 2015

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