Ternary association reactions of H3O+, NO+ and O-2(+center dot) with N-2, O-2, CO2 and H2O. Implications for selected ion flow tube mass spectrometry analyses of air and breath

0555203 - ÚFCH JH 2023 RIV GB eng J - Journal Article
Smith, D. - Španěl, Patrik
Ternary association reactions of H3O+, NO+ and O-2(+center dot) with N-2, O-2, CO2 and H2O. Implications for selected ion flow tube mass spectrometry analyses of air and breath.
Rapid Communications in Mass Spectrometry. Roč. 36, č. 6 (2022), č. článku e9241. ISSN 0951-4198. E-ISSN 1097-0231
R&D Projects: GA ČR(CZ) GA21-25486S
Institutional support: RVO:61388955
Keywords : trace gas-analysis * sift-ms * cluster ions * reagent ions * o2+ * quantification * series
OECD category: Physical chemistry
Impact factor: 2, year: 2022
Method of publishing: Limited access

Rationale The reactions of the reagent ions used for trace gas analysis in selected ion flow tube mass spectrometry (SIFT-MS), R+, viz. H3O+, NO+ and O-2(+), with the major gases in air and breath samples, M, viz. N-2, O-2, CO2 and H2O, are investigated. These reactions are seen to form weakly-bound adduct ions, R+M, by ternary association reactions that must not be mistaken for genuine volatile organic compound (VOC) analyte ions. Methods The ternary association rate coefficients mediated by helium (He) carrier gas atoms, k(3a), have been determined for all combinations of R+ and M, which form R+M adduct ions ranging in m/z from 47 (H3O+N2) to 76 (O2+center dot CO2). This was achieved by adding variable amounts of M (up to 0.5 mbar pressure) into the He carrier gas (pressure of 1.33 mbar) in a SIFT-MS flow tube at 300 K. Parabolic curvature was observed on some of the semi-logarithmic decay curves that allowed the rate coefficients mediated by M molecules, k(3b), to be estimated. Results Values of k(3a) were found to range from 1 x 10(-31) cm(6) s(-1) to 5 x 10(-29) cm(6) s(-1), which form mass spectral R+M ´ghost peaks´ of significant strength when analysing VOCs at parts-per-billion concentrations. It was seen that the R+M adduct ions (except when M is H2O) react with H2O molecules by ligand switching forming the readily recognised monohydrates of the initial reagent cations R+H2O. Whilst this ligand switching diminishes the R+M adduct ghost peaks, it does not eliminate them entirely. Conclusions The significance of these adduct ions for trace gas analysis by SIFT-MS in the low m/z region is alluded to, and some examples are given of m/z spectral overlaps of the R+M and R+H2O adduct cations with analyte cations of VOCs formed by analysis of complex media like exhaled breath, warning that ghost peaks will be enhanced using nitrogen carrier gas in SIFT-MS.
Permanent Link: http://hdl.handle.net/11104/0329721