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High Pressure Mass Spectrometry: The Generation of Mass Spectra at Operating Pressures Exceeding 1 Torr in a Microscale Cylindrical Ion Trap Kenion H. Blakeman, Derek Wolfe, Craig Cavanaugh, and J. Michael Ramsey Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b00706 • Publication Date (Web): 23 Apr 2016 Downloaded from http://pubs.acs.org on April 27, 2016
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Analytical Chemistry
High Pressure Mass Spectrometry: The Generation of Mass Spectra at Operating Pressures Exceeding 1 Torr in a Microscale Cylindrical Ion Trap Kenion H. Blakeman1, Derek W. Wolfe1, Craig A. Cavanaugh2, and J. Michael Ramsey*1,2,3,4 1
Department of Chemistry, 2Department of Applied Physical Sciences, 3Department of
Biomedical Engineering, and 4Carolina Center for Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States AUTHOR EMAIL ADDRESS
[email protected] ABSTRACT We present the first demonstration of high pressure mass spectrometry (HPMS), which we define as mass spectrometry performed at pressures greater than 100 mTorr. Mass analysis is shown at operational pressures exceeding 1 Torr of helium buffer gas. A differentially pumped MS system was constructed for HPMS development consisting of two chambers. The first chamber (mass analysis chamber) was operated at pressures up to 1.2 Torr and contained the ionization source and a microscale cylindrical ion trap (CIT) mass analyzer. The CIT had critical dimensions of r0 = 500 µm and z0 = 650 µm. The second chamber was held at a lower pressure (< 10 mTorr) and contained an electron 1 ACS Paragon Plus Environment
Analytical Chemistry
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multiplier for detection. Mass spectra for xenon, 2-chloroethyl ethyl sulfide (CEES), and octane were acquired with helium buffer gas pressures ranging from 0.04 to 1.2 Torr in the mass analysis chamber. Full-width at half maximum of mass spectral peaks was found to increase 143% for xenon, 40% for CEES, and 77% for octane over this pressure range, with maximum peak widths of 1.19, 1.26, and 0.82 Da, respectively. Data were fitted with an algebraic model that factors in ion-neutral collision peak broadening effects at high pressures. Experimental and theoretical peak broadening slopes showed good agreement at buffer gas pressures greater than 0.2 Torr. Experiments presented here demonstrate mass spectrometry at pressures orders of magnitude higher than conventionally practiced with any type of mass analyzer. The use of HPMS provides a way to eliminate turbo pumping requirements, leading to significant reduction in MS system size, weight, and power and facilitating a path toward compact/handheld mass spectrometers with numerous potential applications.
INTRODUCTION There is considerable interest in portable mass spectrometry (MS) as a tool for field applications where selective, rapid, and sensitive measurements are critical.1,2 Target analytes include chemical warfare agents,3 environmental contaminants,4,5 and toxic industrial compounds.6 Current portable MS technologies are typically suitcase-sized, weigh 13-45 kg, and may include a gas chromatograph. 7–9 These portable MS systems can generally be described as conventional mass spectrometers with basic components including pumps, mass analyzer, and electronics repackaged to minimize size, weight and power (SWaP). Two examples of such instruments are the Guardion-7 and the HAPSITE ER chemical identification system, both of
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Analytical Chemistry
which have GC/MS capabilities. The Guardion-7 has dimensions of 47 x 36 x 18 cm3, weighs 13 kg, and has a battery life of about 4 hours.10,11 In comparison, the HAPSITE ER chemical identification system has dimensions of 46 x 43 x 18 cm3, weighs 19 kg, and has a battery life of 2 to 3 hours.12,13 While these instruments are more compact and portable than laboratory systems, they still have impractical weights and dimensions for a handheld device. Reduction in the size and weight of mass spectrometers to handheld forms has been challenging primarily due to vacuum system requirements, despite the development of miniature turbo and roughing pumps. Many current fieldable mass spectrometry systems push boundaries of MS miniaturization, such as the MMS 100 and OEM-100 from 1st Detect14 and the Griffin 400 series and Griffin 844 from FLIR,15,16 but all of these systems require turbo pumps for operation. With the development of a discontinuous atmospheric pressure interface (DAPI), ion trapping has been performed at elevated pressures (~1 Torr), but a turbo pump is still needed to reach lower pressures for mass analysis (
