A vacuum ultraviolet ion source (VUV-IS) for iodide-chemical ionization mass spectrometry: A substitute for radioactive ion sources

Details

• Journal Title:
  Atmospheric Measurement Techniques
• Personal Author:
  Ji, Yi ; Huey, L. Gregory ; Tanner, David J. ; Lee, Young Ro ; Veres, Patrick R. ; Neuman, J. Andrew ; Wang, Yuhang ; Wang, Xinming
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; CSL (Chemical Sciences Laboratory) ; CIRES (Cooperative Institute for Research in Environmental Sciences)
• Description:
  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 SF−6.
• Keywords:
  Ion Source Radiation Spectrometry Ulraviolet Light Ion Source Ulraviolet Light
• Source:
  Atmos. Meas. Tech., 13, 3683–3696, 2020
• DOI:
  https://doi.org/10.5194/amt-13-3683-2020
• Document Type:
  Journal Article
• Rights Information:
  CC BY
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha256:7fe2f0be2a25baba48be36b722db7341d87696b799372feb4aa691e772d179f3
• Download URL:
  https://repository.library.noaa.gov/view/noaa/29380/noaa_29380_DS1.pdf
• File Type:
  [PDF - 1.58 MB ]