A vacuum ultraviolet ion source (VUV-IS) for iodide–chemical ionization mass spectrometry: a substitute for radioactive ion sources
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Published:2020-07-09
Issue:7
Volume:13
Page:3683-3696
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ISSN:1867-8548
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Container-title:Atmospheric Measurement Techniques
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language:en
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Short-container-title:Atmos. Meas. Tech.
Author:
Ji Yi, Huey L. GregoryORCID, Tanner David J., Lee Young Ro, Veres Patrick R.ORCID, Neuman J. AndrewORCID, Wang YuhangORCID, Wang XinmingORCID
Abstract
Abstract. A new ion source (IS) utilizing vacuum ultraviolet (VUV) light is developed and characterized for use with iodide–chemical ionization mass
spectrometers (I−-CIMS). The VUV-IS utilizes a compact krypton lamp that emits light at two wavelengths corresponding to energies of
∼10.030 and 10.641 eV. The VUV light photoionizes either methyl iodide (ionization potential, IP = 9.54 ± 0.02 eV)
or benzene (IP = 9.24378 ± 0.00007 eV) to form cations and photoelectrons. The electrons react with methyl iodide to form
I−, which serves as the reagent ion for the CIMS. The VUV-IS is characterized by measuring the sensitivity of a quadrupole CIMS (Q-CIMS) to
formic acid, molecular chlorine, and nitryl chloride under a variety of flow and pressure conditions. The sensitivity of the Q-CIMS, with the
VUV-IS, reached up to ∼700 Hz pptv−1, with detection limits of less than 1 pptv for a 1 min integration period. The
reliability of the Q-CIMS with a VUV-IS is demonstrated with data from a month-long ground-based field campaign. The VUV-IS is further tested by
operation on a high-resolution time-of-flight CIMS (TOF-CIMS). Sensitivities greater than 25 Hz pptv−1 were obtained for formic acid and
molecular chlorine, which were similar to that obtained with a radioactive source. In addition, the mass spectra from sampling ambient air was
cleaner with the VUV-IS on the TOF-CIMS compared to measurements using a radioactive source. These results demonstrate that the VUV lamp is a viable
substitute for radioactive ion sources on I−-CIMS systems for most applications. In addition, initial tests demonstrate that the VUV-IS can
be extended to other reagent ions by the use of VUV absorbers with low IPs to serve as a source of photoelectrons for high IP electron attachers,
such as SF6-.
Funder
National Science Foundation U.S. Environmental Protection Agency National Aeronautics and Space Administration
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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