Compendium of the Reactions of H3O+ With Selected Ketones of Relevance to Breath Analysis Using Proton Transfer Reaction Mass Spectrometry

Abstract

Soft chemical ionization mass spectrometric techniques, such as proton transfer reaction mass spectrometry (PTR-MS), are often used in breath analysis, being particularly powerful for real-time measurements. To ascertain the type and concentration of volatiles in exhaled breath clearly assignable product ions resulting from these volatiles need to be determined. This is difficult for compounds where isomers are common, and one important class of breath volatiles where this occurs are ketones. Here we present a series of extensive measurements on the reactions of H 3 O + with a selection of ketones using PTR-MS. Of particular interest is to determine if ketone isomers can be distinguished without the need for pre-separation by manipulating the ion chemistry through changes in the reduced electric field. An additional issue for breath analysis is that the product ion distributions for these breath volatiles are usually determined from direct PTR-MS measurements of the compounds under the normal operating conditions of the instruments. Generally, no account is made for the effects on the ion-molecule reactions by the introduction of humid air samples or increased CO 2 concentrations into the drift tubes of these analytical devices resulting from breath. Therefore, another motivation of this study is to determine the effects, if any, on the product ion distributions under the humid conditions associated with breath sampling. However, the ultimate objective for this study is to provide a valuable database of use to other researchers in the field of breath analysis to aid in analysis and quantification of trace amounts of ketones in human breath. Here we present a comprehensive compendium of the product ion distributions as a function of the reduced electric field for the reactions of H 3 O + . (H 2 O) n ( n = 0 and 1) with nineteen ketones under normal and humid (100% relative humidity for 37 °C) PTR-MS conditions. The ketones selected for inclusion in this compendium are (in order of increasing molecular weight): 2-butanone; 2-pentanone; 3-pentanone; 2-hexanone; 3-hexanone; 2-heptanone; 3-heptanone; 4-heptanone; 3-octanone; 2-nonanone; 3-nonanone; 2-decanone; 3-decanone; cyclohexanone; 3-methyl-2-butanone; 3-methyl-2-pentanone; 2-methyl-3-pentanone; 2-methyl-3-hexanone; and 2-methyl-3-heptanone.

Formation of positive product ions from substances with low proton affinity in high kinetic energy ion mobility spectrometry

“…At thermal ion–molecule interaction energies, extensive information is available from selected ion flow tube mass spectrometry studies concerning the reactions of H 3 O + , NO + , and O 2 + with various analyte molecules 25–39 . Furthermore, PTR‐MS 40,41 and selective reagent ionization time‐of‐flight‐MS 42,43 studies deliver information at elevated ion–molecule interaction energies. According to these studies, various ionization pathways are possible in HiKE‐IMS, ranging from simple charge transfer to chemical reactions such as proton transfer or ligand switching, which may result in the formation of multiple product ion species per analyte molecule species.…”

Monoterpene Chemical Speciation with High Time Resolution Using a FastGC/PTR-MS: Results from the COV3ER Experiment on Quercus ilex

“…This prototype is a modified version of the setup used by Ruzsanyi et al (2013) [29] and Romano et al (2014) [20]. It is described in Malásková et al (2019) [30]. Briefly, a 10 m nonpolar dimethyl polysiloxane column (MXT1, RESTEK, Bellefonte, PA, USA) with an internal diameter (I.D.)…”

“…They included the need of very low dwell times narrowing the amount of monitored masses, the higher dilution due to the higher flow inside the PTR-MS drift-tube and the necessity to adapt a number of control elements, since the normal PTR-ToF-MS input/output system is not available. The latter was the main adaptation made in this setup, compared with the one described in Malásková et al (2019) [30], where this FastGC prototype was coupled to a PTR-ToF-MS. In gas chromatography, the efficiency of the separation and the quality of the resulting chromatograms can be influenced by several operational parameters, such as temperature and carrier gas flow rates.…”

Real-Time Non-Invasive Monitoring of Short-Chain Fatty Acids in Exhaled Breath

“…The proton transfer can be both dissociative and non-dissociative. Fragmentation of protonated molecules can occur spontaneously or originate from collision-induced reactions of the reagent ions with (charged) analytes (Malásková et al, 2019b). Therefore, the mass spectrum of a single compound may be composed of the protonated molecule, as well as fragment ions derived from the parent molecule.…”