Oral Presentation AUS-oMicS 2025

Unimolecular Decomposition of Deprotonated Glyphosate: Ion Mobility Mass Spectrometry to Discern Cyclic versus Linear Dehydration Products (#70)

Olivia Rusli 1 , Nicole Rijs 1
  1. School of Chemistry, UNSW Sydney, Sydney, NSW, Australia

Gas phase studies of glyphosate, a globally ubiquitous herbicide, can provide insights intro thermal degradation pathways.1 Many conditions in the gas phase, including (de)protonation and cationization can result in structural complexity that is challenging to analyse.2 Deprotonated glyphosate follows several fragmentation pathways as previously observed by multistage mass spectrometry and collision-induced dissociation (CID) by Goodwin et al.3,4 The fragmentation pathways include decarboxylation and dehydration which further leads to the formation of characteristic fragments and isomeric product ions, depending on the pathways. For the first time, ion mobility-mass spectrometry (IM-MS) has been used to identify the isomers of dehydrated glyphosate. The previously proposed cyclic and linear isomers of dehydrated deprotonated glyphosate were confirmed using their mobility-selected fragmentation patterns, their DFT structures and their collision cross sections. Although the mobility spectrum for the dehydrated fragment wasn’t baseline resolved, IM characterisation of each isomer was possible through the extraction of the arrival time distribution of their characteristic fragments. This work highlights the ability to separate isomers using ion mobility-mass spectrometry and tandem mass spectrometry, even when the isomers aren’t baseline resolved. In addition, the unusual gas phase PO4- ion was observed. This is believed to be an ion-molecule reaction product between the PO3- ion and background water within the travelling wave ion mobility (TWIMS) cell resulting in oxygen atom transfer and H2 elimination.

(1)        Narimani, M.; da Silva, G. Environmental Science: Processes & Impacts 2020, 22 (1), 152–160. https://doi.org/10.1039/C9EM00422J.

(2)        Rusli, O. et al.  Phys. Chem. Chem. Phys. 2024. https://doi.org/10.1039/D4CP04019H.

(3)        Goodwin, L.; Startin, J. R.; Goodall, D. M.; Keely, B. J.  Rapid Communications in Mass Spectrometry 2003, 17 (9), 963–969. https://doi.org/10.1002/rcm.1007.

(4)        Goodwin, L.; Startin, J. R.; Goodall, D. M.; Keely, B. J.  Rapid Communications in Mass Spectrometry 2004, 18 (1), 37–43. https://doi.org/10.1002/rcm.1264.