The peppermint breath test benchmark for PTR-MS and SIFT-MS

18openInternationalInternational coauthor/editorA major challenge for breath research is the lack of standardization in sampling and analysis. To address this, a test that utilizes a standardized intervention and a defined study protocol has been proposed to explore disparities in breath research across different analytical platforms and to provide benchmark values for comparison. Specifically, the Peppermint Experiment involves the targeted analysis in exhaled breath of volatile constituents of peppermint oil after ingestion of the encapsulated oil. Data from the Peppermint Experiment performed by proton transfer reaction mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry (SIFT-MS) are presented and discussed herein, including the product ions associated with the key peppermint volatiles, namely limonene, α- and β-pinene, 1,8-cineole, menthol, menthone and menthofuran. The breath washout profiles of these compounds from 65 individuals were collected, comprising datasets from five PTR-MS and two SIFT-MS instruments. The washout profiles of these volatiles were evaluated by comparing the log-fold change over time of the product ion intensities associated with each volatile. Benchmark values were calculated from the lower 95% confidence interval of the linear time-to-washout regression analysis for all datasets combined. Benchmark washout values from PTR-MS analysis were 353 min for the sum of monoterpenes and 1,8-cineole (identical product ions), 173 min for menthol, 330 min for menthofuran, and 218 min for menthone; from SIFT-MS analysis values were 228 min for the sum of monoterpenes, 281 min for the sum of monoterpenes and 1,8-cineole, and 370 min for menthone plus 1,8-cineole. Large inter- and intra-dataset variations were observed, whereby the latter suggests that biological variability plays a key role in how the compounds are absorbed, metabolized and excreted from the body via breath. This variability seems large compared to the influence of sampling and analytical procedures, but further investigations are recommended to clarify the effects of these factors.openHenderson, Ben; Slingers, Gitte; Pedrotti, Michele; Pugliese, Giovanni; Malásková, Michaela; Bryant, Luke; Lomonaco, Tommaso; Ghimenti, Silvia; Moreno, Sergi; Cordell, Rebecca; Harren, Frans J M; Schubert, Jochen; Mayhew, Chris A; Wilde, Michael; Di Francesco, Fabio; Koppen, Gudrun; Beauchamp, Jonathan D; Cristescu, Simona MHenderson, B.; Slingers, G.; Pedrotti, M.; Pugliese, G.; Malásková, M.; Bryant, L.; Lomonaco, T.; Ghimenti, S.; Moreno, S.; Cordell, R.; Harren, F.J.M.; Schubert, J.; Mayhew, C.A.; Wilde, M.; Di Francesco, F.; Koppen, G.; Beauchamp, J.D.; Cristescu, S.M

Proton Transfer Reaction-Mass Spectrometry and its Applications to Breath Research

Thesis was written in English, therefore only English abstract is provided.Proton Transfer Reaction Mass Spectrometry (PTR-MS) has been used in breath research for almost 25 years, but many details of product ions resulting from the reaction of H3O+ with breath volatile compounds of importance are missing. This data is important to have in order to identify such compounds in complex chemical environments, such as exhaled breath. However, the identification of the product ions that can be used to identify a compound is complicated, because PTR-MS users use different operational parameters, with the most important being the value of the reduced electric field, namely the ratio of the electric field E to the buffer gas number density, N, which defines ion-molecule collisional energies along the drift tube region. Furthermore, given that the m/z ratio of a product ion is used to identify a compound, there is always some doubt in the assignment. However, by operating at different E/N values different product ions are produced, which can aid in identifying the compound with a higher confidence. For these reasons, the work presented in this thesis has investigated the proton transfer reactions occurring in the PTR-MS as a function of E/N, in order to inform users what are the reduced electric fields best used. Furthermore, given that the humidity of the buffer gas in the drift tube causes changes in the reagent ions, and given that breath is humid, all measurements reported here have been undertaken under what is referred to as either “normal” and “humid” drift tube conditions, with the latter being required to mimic breath samples. The interpretation of the experimental results have been aided by quantum mechanical calculations, which are also presented in the thesis. Three main studies resulted in three peer-reviewed papers. The first study provides information on the product ions resulting from the reactions of H3O+ with a series of ketones, which showed us that the effect of different humidity varies for different compounds and in many cases, less fragmentation was observed for samples with higher humidity. The second study provides an investigation of the key volatiles contained in peppermint oil, of relevance to pharmacokinetic breath studies, which apart from reporting product ions as a function of reduced electric field, highlights the difficulties of unambiguously identifying trace volatiles on breath and demonstrates issues of surface effects that leads to temporal effects on concentrations. The third and final study presents results on a number of fluranes; isoflurane, enflurane, desflurane and sevoflurane, all used as inhalation anaesthetics. This study is required for a clinical study currently being undertaken which is investigating the duration of anaesthetics in the body after surgery. The quantum mechanical calculations that have been undertaken on these fluranes show that their proton affinities are less than that of water, and yet are detected with a high sensitivity. This is possible because proton transfer is driven by electric field heating and the spontaneous dissociation of the protonated species so that a back reaction with water is not possible.Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersArbeit an der Bibliothek noch nicht eingelangt - Daten nicht geprüftInnsbruck, Univ., Diss., 2020(VLID)473236

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

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 H3O+ 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 CO2 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 H3O+. (H2O)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.(VLID)4826166Version of recor

A benchmarking protocol for breath analysis: The peppermint experiment

International audienceSampling of volatile organic compounds (VOCs) has shown promise for detection of a range of diseases but results have proved hard to replicate due to a lack of standardization. In this work we introduce the 'Peppermint Initiative'. The initiative seeks to disseminate a standardized experiment that allows comparison of breath sampling and data analysis methods. Further, it seeks to share a set of benchmark values for the measurement of VOCs in breath. Pilot data are presented to illustrate the standardized approach to the interpretation of results obtained from the Peppermint experiment. This pilot study was conducted to determine the washout profile of peppermint compounds in breath, identify appropriate sampling time points, and formalise the data analysis. Five and ten participants were recruited to undertake a standardized intervention by ingesting a peppermint oil capsule that engenders a predictable and controlled change in the VOC profile in exhaled breath. After collecting a pre-ingestion breath sample, five further samples are taken at 2, 4, 6, 8, and 10 h after ingestion. Samples were analysed using ion mobility spectrometry coupled to multi-capillary column and thermal desorption gas chromatography mass spectrometry. A regression analysis of the washout data was used to determine sampling times for the final peppermint protocol, and the time for the compound measurement to return to baseline levels was selected as a benchmark value. A measure of the quality of the data generated from a given technique is proposed by comparing data fidelity. This study protocol has been used for all subsequent measurements by the Peppermint Consortium (16 partners from seven countries). So far 1200 breath samples from 200 participants using a range of sampling and analytical techniques have been collected. The data from the consortium will be disseminated in subsequent technical notes focussing on results from individual platforms