High-pressure cylindrical ion trap mass spectrometry Public Deposited

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  • March 21, 2019
Creator
  • Wolfe, Derek
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • This work describes the development of mass spectrometry (MS) instrumentation capable of operating at helium buffer gas pressures up to 1 torr. This is approximately three orders of magnitude higher than the pressures used in commercially available MS instrumentation. High-pressure operation is desirable since it reduces the size, weight, and power (SWaP) of the instrument by reducing the pumping system workload. A simple and rugged roughing pump could achieve these pressures while reducing SWaP by eliminating the turbo pump. Therefore this technology could be used to develop next generation hand-portable instruments and bring MS to new applications. Custom MS instrumentation was designed and built to utilize 500 μm radius cylindrical ion trap (CIT) mass analyzers. Two vacuum chamber configurations were used to establish a performance baseline at traditional ion trap operating pressures. The instrument design was refined during these simple experiments before moving to high-pressure operation. The feasibility of high-pressure CIT operation up to 1 torr was first demonstrated using a differentially pumped instrument. Electron ionization was performed and a mass-selective instability scan was used to eject ions into a low-pressure chamber for detection with an electron multiplier. Peak broadening effects at high pressure were reduced by increasing axial RF amplitude and ejecting ions into a low-pressure detection region. Peak widths for Xe+ spectra at pressures from 38.6 to 983.5 mTorr were analyzed and average peak widths for these low and high-pressure spectra were found to be relatively constant. After demonstrating the CIT operation at high pressure, it was desirable to replace the electron multiplier with a pressure tolerant detector and simplify the instrument to a single vacuum chamber. The first experimental investigation of MS in this isobaric chamber at pressures up to 867 mTorr is reported. A solid-state capacitive transimpedance amplifier (CTIA) was used for ion detection at high pressures. Average peak widths for Xe+ ions in spectra acquired at pressures from 133 to 867 mTorr were found to be nearly constant. Results presented here demonstrate mass spectra at ~1 torr using a solid-state ion detector capable of operating at atmospheric pressure for MS applications requiring portability.
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  • In Copyright
Advisor
  • Ramsey, J. Michael
Degree
  • Doctor of Philosophy
Graduation year
  • 2012
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