Preprints
https://doi.org/10.5194/egusphere-2024-16
https://doi.org/10.5194/egusphere-2024-16
12 Jan 2024
 | 12 Jan 2024

Response of protonated, adduct, and fragmented ions in Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS)

Fangbing Li, Dan Dan Huang, Linhui Tian, Bin Yuan, Wen Tan, Liang Zhu, Penglin Ye, Douglas Worsnop, Ka In Hoi, Kai Meng Mok, and Yong Jie Li

Abstract. Volatile organic compounds (VOCs) affect secondary pollutant formation via active chemistry. Proton-transfer-reaction mass spectrometry (PTR-MS) is one of the most important techniques to study the highly variable spatial and temporal characteristics of VOCs. The response of protonated, adduct, and fragmented ions in PTR-MS in changing instrument settings and varying relative humidity (RH) requires rigorous characterization. Herein, dedicatedly designed laboratory experiments were conducted to investigate the response of these ions for 21 VOCs, including 12 oxygenated VOCs and two nitriles, using the recently developed Vocus PTR-MS. Our results show that the focusing ion-molecule reactor (FIMR) axial voltage increases sensitivity by three to four orders of magnitude but does not significantly change the fractions of protonated ions. Reducing the FIMR pressure, however, substantially increases fragmentation. Applying a high radio frequency (RF) amplitude radially on FIMR can enhance sensitivity by one to two orders of magnitude without affecting the protonated ion fractions. The change in big segmented quadrupole (BSQ) amplitude mainly affects sensitivity and protonated ion fraction by modifying ion transmission. The relationship between sensitivity and proton-transfer reaction rate constant is complicated by the influences from both ion transmission and protonated ion fraction. The protonated ions of most VOCs studied (19 out of 21) show less than 15 % variations in sensitivity as RH increases from ~5 % to ~85 %, except for some long-chain aldehydes which show a positive RH variation of up to 30 %. Our results suggest that the Vocus PTR-MS can reliably quantify the majority of VOCs under ambient conditions with varying RH. However, caution is advised for small oxygenates such as formaldehyde and methanol due to their low sensitivity, as well as for long-chain aldehydes for their slight RH dependence and fragmentation.

Fangbing Li, Dan Dan Huang, Linhui Tian, Bin Yuan, Wen Tan, Liang Zhu, Penglin Ye, Douglas Worsnop, Ka In Hoi, Kai Meng Mok, and Yong Jie Li

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-16', Anonymous Referee #1, 15 Feb 2024
  • RC2: 'Reviewer comment on egusphere-2024-16', Anonymous Referee #2, 15 Feb 2024
    • AC2: 'Reply on RC2', Yong Jie Li, 26 Feb 2024
Fangbing Li, Dan Dan Huang, Linhui Tian, Bin Yuan, Wen Tan, Liang Zhu, Penglin Ye, Douglas Worsnop, Ka In Hoi, Kai Meng Mok, and Yong Jie Li
Fangbing Li, Dan Dan Huang, Linhui Tian, Bin Yuan, Wen Tan, Liang Zhu, Penglin Ye, Douglas Worsnop, Ka In Hoi, Kai Meng Mok, and Yong Jie Li

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Short summary
The response of protonated, adduct, and fragmented ions of 21 volatile organic compounds (VOCs) was investigated with varying instrument setting and relative humidity (RH) in a Vocus proton-transfer-reaction mass spectrometer (PTR-MS). The protonated ions of most VOCs studied show < 15 % variations in sensitivity, except for some long-chain aldehydes. The relationship between sensitivity and PTR rate constant is complicated by the influences from ion transmission and protonated ion fraction.