Using chemical ionisation in the identification of volatile organic compounds (VOCs) on breath
Brett O’Brien*(2), Tilly Woodland(2), Karin Rosenkilde Laursen(1), Kirsten Østergaard(1), Chad Schaber(2), Owen Birch(2), Danial Mead(2), Mads Mørk Jensen(3), Merete Bilde(3), Søren K. Kjærgaard(1), The Climate Chamber Group(1), Max Allsworth(2), Billy Boyle (2), Torben Sigsgaard(1), Agnieszka Smolinska(2).
1. Environment, Occupation and Health, Department of Public Health, Aarhus University, Denmark.
2. Owlstone Medical, Cambridge, UK.
3. Department of Chemistry, Aarhus University, Denmark.
Abstract: Indoor air pollution-induced lung damage is associated with respiratory and cardiovascular diseases and was responsible for an estimated 3.2 million deaths in 2020 (WHO, 2022). Candle Study 1 (CS1) at Owlstone Medical Ltd (OML) aims to investigate volatile organic compounds (VOCs) associated with lung inflammation induced by acute exposure to emissions from different candles. Asthmatic patients (n=17) participated in a randomized controlled double-blind crossover study including two exposure sessions: air mixed with emissions from two different candles for five hours. A gas chromatography high resolution mass spectrometry (GCMS) approach (Breath Biopsy®) was used to collect and analyse samples. Analysis involved an untargeted method as well as targeted analysis of 23 compounds, which were quantified using calibration curves. Untargeted analysis was performed using Compound Discoverer software. Fifteen VOCs in exhaled breath showed statistically significant differences between pre-exposure and immediate post-exposure samples. Tentative structural assignments were generated for fourteen of the MFs using spectral alignment with internal VOC libraries and NIST libraries. Samples were re-analysed by GCMS in positive chemical ionisation (PCI) mode using methane as reagent gas, to generate robust pseudomolecular ion (M+H) signals for eight of the MFs thereby elucidating their molecular formulas. Furthermore, the effects of reagent gas, flow rate, electron energy, source temperature and MS polarity on CI signals were explored. Using spectral information and retention indexing of authentic standards, fourteen of the fifteen MF assignments were verified and included aldehydes, ketones, alkene sulfides, furans and a terpene. This work has demonstrated the ability of CI analysis to aid the structural identification and elucidation of VOC biomarkers on breath.