Preprints
https://doi.org/10.5194/amt-2021-164
https://doi.org/10.5194/amt-2021-164

  07 Jun 2021

07 Jun 2021

Review status: a revised version of this preprint is currently under review for the journal AMT.

Quantification of Isomer-Resolved Iodide CIMS Sensitivity and Uncertainty Using a Voltage Scanning Approach

Chenyang Bi1, Jordan E. Krechmer2, Graham O. Frazier1, Wen Xu2, Andrew T. Lambe2, Megan S. Claflin2, Brian M. Lerner2, John T. Jayne2, Douglas R. Worsnop2, Manjula R. Canagaratna2, and Gabriel Isaacman-VanWertz1 Chenyang Bi et al.
  • 1Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia, 24060, USA
  • 2Aerodyne Research Inc, Billerica, Massachusetts, 01821, USA

Abstract. Chemical ionization mass spectrometry (CIMS) using iodide as a reagent ion has been widely used to classify organic compounds in the atmosphere by their elemental formula. Unfortunately, calibration of these instruments is challenging due to a lack of commercially available standards for many compounds, which has led to the development of methods for estimating CIMS sensitivity. By coupling a Thermal desorption Aerosol Gas chromatograph (TAG) simultaneously to a flame ionization detector (FID) and an iodide CIMS, we use the individual particle-phase analytes, quantified by the FID, to examine the sensitivity of the CIMS and its variability between isomers of the same elemental formula. Iodide CIMS sensitivities of isomers within a formula are found to generally vary by one order of magnitude with a maximum deviation of two orders of magnitude. Furthermore, we compare directly measured sensitivity to a method of estimating sensitivity based on declustering voltage (i.e., “voltage scanning”). This approach is found to carry high uncertainties for individual analytes (half to one order of magnitude), but represents a central tendency that can be used to estimate the sum of analytes with reasonable error (~30 % differences between predicted and measured moles). Finally, GC retention time, which is associated with vapor pressure and chemical functionality of an analyte, is found to qualitatively correlate with iodide CIMS sensitivity, but the relationship is not close enough to be quantitatively useful and could be explored further in the future as a potential calibration approach.

Chenyang Bi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-164', Anonymous Referee #1, 16 Jun 2021
    • AC1: 'Reply on RC1', Chenyang Bi, 10 Sep 2021
  • RC2: 'Comment on amt-2021-164', Anonymous Referee #2, 13 Jul 2021
    • AC2: 'Reply on RC2', Chenyang Bi, 10 Sep 2021

Chenyang Bi et al.

Chenyang Bi et al.

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Short summary
Iodide-adduct chemical ionization mass spectrometry (I-CIMS) has been widely used to analyze airborne organics. In this study, I-CIMS sensitivities of isomers within a formula are found to generally vary by one and up to two orders of magnitude. Comparisons between measured and predicted moles, obtained using a voltage-scanning calibration approach, show that predictions for individual compounds or formulas might carry high uncertainty, yet the summed moles of analytes agree reasonably well.