Direct analysis of aldehydes and carboxylic acids in the gas phase by negative ionization selected ion flow tube mass spectrometry: Quantification and modelling of ion–molecule reactions

Autor: Sylvie Lacombe, Jean-Marc Sotiropoulos, N. Costarramone, Mylène Ghislain, Mickael Le Bechec, Thierry Pigot, Robin Van Den Berg
Rok vydání: 2019
Předmět:
Zdroj: Rapid Communications in Mass Spectrometry. 33:1623-1634
ISSN: 1097-0231
0951-4198
DOI: 10.1002/rcm.8504
Popis: Rationale The concentrations of aldehydes and volatile fatty acids have to be controlled because of their potential harmfulness in indoor air or relationship with the organoleptic properties of agri-food products. Although several specific analytical methods are currently used, the simultaneous analysis of these compounds in a complex matrix remains a challenge. The combination of positive and negative ionization selected ion flow tube mass spectrometry (SIFT-MS) allows the accurate, sensitive and high-frequency analysis of complex gas mixtures of these compounds. Methods The ion-molecule reactions of negative precursor ions (OH- , O•- , O2 •- , NO2 - and NO3 - ) with five aldehydes and four carboxylic acids were investigated in order to provide product ions and rate constants for the quantification of these compounds by negative ion SIFT-MS. The results were compared with those obtained by conventional analysis methods and/or with already implemented SIFT-MS positive ionization methods. The modelling of hydroxide ion (OH- )/molecule reaction paths by ab-initio calculation allowed a better understanding of these gas-phase reactions. Results Deprotonation systematically occurs by reaction between negative ions and aldehydes or acids, leading to the formation of [M - H]- primary ions. Ab-initio calculations demonstrated the α-CH deprotonation of aldehydes and the acidic proton abstraction for fatty acids. For aldehydes, the presence of water in the flow tube leads to the formation of hydrated ions, [M - H]- .H2 O. With the NO2 - precursor ion, a second reaction channel results in ion-molecule association with the formation of M.NO2 - ions. Conclusions Except for formaldehyde, all the studied compounds can be quantified by negative ion SIFT-MS with significant rate constants. In addition to positive ion SIFT-MS with H3 O+ , O2 + and NO+ precursor ions, negative ionization with O•- , O2 •- , OH- , NO2 - and NO3 - extends the range of analysis of aldehydes and carboxylic acids in air without a preparation or separation step. This methodology was illustrated by the simultaneous quantification in single-scan experiments of seven aldehydes and six carboxylic acids released by building materials.
Databáze: OpenAIRE
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