Abstrakt
Introduction: Glyoxal (m.w. 58 g/mol) is a highly reactive molecule associated with some basic biological processes [1], photocatalysis of CO2 into CH4 on TiO2 or photo-dissociation of anthropogenic and biogenic volatile organic compounds (VOC) [3]. Presence of glyoxal can be monitored using soft chemical ionization mass spectrometry (SCI-MS).
Here we discuss the ion chemistry of glyoxal interacting with H3O+, NO+ and O2.+ reagent ions used in SCI-MS and possibility of detection. Methods: Selected ion flow tube mass spectrometry, SIFT-MS[4], was used to investigate ion-molecule reactions of H3O+, NO+ and O2.+ reagent ions with glyoxal at variable humidity.
The ion chemistry under thermal conditions is theoretically described using B3LYP/6-311(p,d) calculations and using numerical modelling of the ion-molecule reaction kinetics. Results: NO+ reactionslead to formation of C2H2O2(NO)+ and C2H2O2+ ions, in the humid environment the association reaction is dominant.
Charge transfer was observed for O2+ reactions as well. Additional dissociation observed previously for O2+ reagent ion was not confirmed [5-6].
The H3O+ reactionproceeds at dry conditions via proton transfer reaction forming C2H3O2+. With increasing concentration of water molecules, formation of m/z 31 (CH2OH+) is becoming dominant.
Corresponding hydrated ions were observed as well. Using quantum chemistry calculations, we estimated PA(C2H2O2) = 165.1 kcal/moland characterised the energetics of reaction pathways formingCH2OH+.
Reaction kinetics modelling indicatesformation of a stable intermediate C2H3O2+.H2O which dissociates to protonated formaldehyde CH2OH+ after interaction with water. Conclusions: According to theory,protonated formaldehyde is formedfromC2H3O2+.H2O by reaction with water resulting into CH2OH+ + HCOOH + H2O products or by a formation of exited C2H3O2+.H2O* after two body association whichdissociatesto CH2OH+ directly.
Finally, protonated formaldehyde hydrate is not the terminating ionathigh humilities. Thus, we expect a catalytic effect of CH2OH+.H2O forming a proton boundwater dimeras CH2OH+.H2O + H2O RIGHTWARDS ARROW CH2O + H3O+.H2O.
Novel Aspect: Understanding of ion chemistry of glyoxal is important for itsanalysisin gas phaseusing SCI-MS techniques and itsdistinguishing from isobaric compounds.