Preprints
https://doi.org/10.5194/amt-2021-22
https://doi.org/10.5194/amt-2021-22

  06 Apr 2021

06 Apr 2021

Review status: a revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Effects of Aerosol Size and Coating Thickness on the Molecular Detection using Extractive Electrospray Ionization

Chuan Ping Lee1, Mihnea Surdu1, David M. Bell1, Houssni Lamkaddam1, Mingyi Wang2,3, Farnoush Ataei6, Victoria Hofbauer2,3, Brandon Lopez2,4, Neil M. Donahue2,3,4,5, Josef Dommen1, Andre S. H. Prevot1, Jay G. Slowik1, Dongyu Wang1, Urs Baltensperger1, and Imad El Haddad1 Chuan Ping Lee et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland
  • 2Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
  • 3Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
  • 4Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
  • 5Department of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
  • 6Leibniz-Institute for Tropospheric Research, 04318 Leipzig, Germany

Abstract. Extractive electrospray ionization (EESI) is a well-known technique for high throughput online molecular characterization of chemical reaction products and intermediates, detection of native biomolecules, in vivo metabolomics, and environmental monitoring with negligible thermal and ionization-induced fragmentation for over two decades. However, the EESI extraction mechanism remains uncertain. Prior studies disagree whether analyte particles between 20 and 400 nm diameter are fully extracted or if the extraction is limited to the surface layer. Here, we examined the analyte extraction mechanism by assessing the influence of analyte particle size and coating thickness on the detection of the molecules therein. We find that analyte particles are extracted fully: Organics-coated NH4NO3 particles with a fixed core volume (156 and 226 nm in diameter without coating) show constant signals for NH4NO3 independent of the shell coating thickness, while the signals of the secondary organic molecules comprising the shell varied proportionally to the shell volume. We also find that the EESI sensitivity exhibits a strong size dependence, with an increase in sensitivity by one to three orders of magnitude as analyte particle size decreases from 300 nm to 30 nm. This dependence varies with the electrospray (ES) droplet size and the analyte particle residence time in the EESI inlet, suggesting that the EESI sensitivity is influenced by the coagulation rates between analyte particles and ES droplets. Overall, our results indicate that, in the EESI, analyte particles are fully extracted by the ES droplets regardless of the chemical composition, when they are collected by the ES droplets. However, their coalescence is not complete and depends strongly on their size. This size-dependence is especially relevant when EESI is used to probe size-varying analyte particles as is the case in aerosol formation and growth studies with size ranges below 100 nm, while it does not significantly influence the detection of ambient aerosol dominated by particle sizes ranging between 100–2500 nm, i.e. the accumulation mode.

Chuan Ping Lee et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-22', Anonymous Referee #2, 20 Apr 2021
    • AC1: 'Reply on RC1', Imad El Haddad, 06 Jul 2021
  • RC2: 'Comment on amt-2021-22', Anonymous Referee #1, 04 May 2021
    • AC2: 'Reply on RC2', Imad El Haddad, 06 Jul 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-22', Anonymous Referee #2, 20 Apr 2021
    • AC1: 'Reply on RC1', Imad El Haddad, 06 Jul 2021
  • RC2: 'Comment on amt-2021-22', Anonymous Referee #1, 04 May 2021
    • AC2: 'Reply on RC2', Imad El Haddad, 06 Jul 2021

Chuan Ping Lee et al.

Chuan Ping Lee et al.

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Short summary
The extractive electrospray ionization mass spectrometry (EESI-MS) has been deployed for high throughput online detection of analyte particles with minimal fragmentations for decades. Our studies elucidate the extraction mechanism between analyte particles of different properties and charged electrospray droplets at different sizes. The results show that the extraction is a complete coalesce but is limited by the coalesce efficiency at different sizes, affecting the quantification accuracy.