In this study, we analyzed VOC profiles in ambient room air at five locations commonly used for breath sample collection to better understand the impact of background VOC levels on the analysis. breath.
The separation of the ambient air samples in the five different locations was observed. With the exception of 3-keel which was present in all areas studied, the separation was due to different VOCs, giving each location a specific signature. In the endoscopy assessment area, the VOCs driving separation were primarily monoterpenes, such as β-pinene, and alkanes, such as dodecane, undecane, and tridecane, which are commonly found in essential oils commonly used in cleaning products.13. Given the frequency with which the endoscopy unit is cleaned, it is likely that these VOCs are the result of frequent cleaning processes in this space. In the clinical research bay, as with endoscopy, separation was primarily due to monoterpenes, such as α-pinene, also most likely from cleaning products. In the operating room, the VOC signature was mainly made up of branched alkanes. These compounds can come from surgical instruments because they are abundant in oils and lubricants14. In the surgical outpatient clinic, characteristic VOCs included a selection of alcohols: 1-nonanol, present in vegetable oil and therefore cleaning products, and benzyl alcohol, present in perfumes and local anesthetics.15,16,17,18. VOCs within the mass spectrometry laboratory were largely different from other areas, which was to be expected given that this was the only non-clinical area assessed. While some monoterpenes were present, a more homogeneous group of compounds separated this area from the others (2‚2‚2-trifluoro-N-methyl-acetamide‚ pyridine, branched undecane, 2-pentyl-furan‚ ethylbenzene, furfural, anisate d ethyl, o-xylene, m-xylene, isopropyl alcohol and 3-carene), including aromatic hydrocarbons and alcohols. Some of these VOCs may be secondary to the chemicals used in the lab, which is made up of seven mass spectrometry systems operating in both TD and liquid injection modes.
A strong separation of ambient air and breath samples was observed thanks to the PLS-DA, driven by 62 of the 113 VOCs detected. In ambient air, these VOCs were exogenous and included diisopropyl phthalate, benzophenone, acetophenone, and benzyl alcohol, all of which are commonly used in plasticizers and perfumes.19,20,21,22the latter being found in cleaning products16. The chemicals identified in the breath were a mixture of endogenous and exogenous VOCs. Endogenous VOCs consisted largely of branched alkanes which are an established byproduct of lipid peroxidation23 and isoprene, a byproduct of cholesterol synthesis24. Exogenous VOCs included monoterpenes such as β-pinene and D-limonene, which can be traced to citrus essential oils (also commonly used in cleaning products) and food preservatives.13.25. 1-propanol can be both endogenous, deriving from the degradation of amino acids, and exogenous, present in disinfectants26. Of the VOCs that have been found at higher levels in ambient air compared to breath, several have been suggested as possible biomarkers of disease. Ethylbenzene has been shown to be a potential biomarker for several respiratory conditions including lung cancer, COPD27 and pulmonary fibrosis28. N-dodecane and xylene have also been shown to be higher in patients with lung cancer than in those without.29 and m-cymene was found to be higher in patients with active ulcerative colitis30. Therefore, even though ambient air differences do not appear to affect overall respiratory profiles, they could influence the specific VOC levels of interest, concluding that background ambient air monitoring may still be essential.
A separation between ambient air samples taken in the morning and afternoon was also observed. Morning samples were primarily characterized by branched alkanes, commonly found exogenously in cleaning products and waxes31. The four clinical areas included in this study were all cleaned prior to ambient air sampling, which would explain this. The clinical areas were all separated by different VOCs, so this separation cannot be attributed to cleaning. The afternoon samples generally had a mixture of alcohols, hydrocarbons, esters, ketones and aldehydes at higher levels compared to the morning samples. 1-Propanol and phenol can both be present in disinfectants26.32, which is expected given the regular cleaning carried out in the clinical areas during the day. The breath was collected only in the morning. This is due to the multiple other factors that can influence the level of VOCs in the breath during the day that cannot be controlled. This includes consuming food and beverages prior to breath sampling33.34 and different exercise levels35.36.
VOC analysis remains an evolutionary frontier in the development of non-invasive diagnostics. Sampling standardization remains an issue, but our analysis reassuringly demonstrates no significant difference between breath samples taken at different locations. In this study, we demonstrated that VOCs in ambient air vary with location and time of day. However, our results also demonstrate that this does not significantly alter the profile of VOCs in exhaled breath, suggesting that breath sampling can be performed at different locations without significantly impacting the results. Inclusion of multiple locations over a longer period of time and collection of duplicate samples were prioritized. Finally, the separation of ambient air from different locations and the lack of separation in respiration clearly suggest that sampling location does not have a significant impact on the composition of human respiration. This is reassuring for breath analysis studies because it removes a potential confounder for the normalization of breath collection. Although having all breath samples from a single subject is a limitation of our study, it has the potential to reduce the variance of other confounders influenced by human behavior. The single-subject study design has already been used successfully in several studies37. However, further analyzes are needed to draw firm conclusions. Routine ambient air sampling alongside breath sampling is always recommended, to allow exclusion of exogenous compounds and identification of specific contaminants. We recommend the exclusion of isopropyl alcohol given its prevalence in cleaning products, especially in healthcare settings. This study was limited by the number of breath samples taken at each location and further work is needed with a larger number of breath samples to confirm that there is no significant impact on the composition of human breath on the background environment in which it is sampled. Additionally, relative humidity (RH) data have not been collected and although we recognize that RH differentiations could influence the distribution of VOCs, in large scale studies the logistical challenge is significant. both for RH monitoring and for RH data collection.
In conclusion, our study demonstrated that there is variation in VOCs in ambient ambient air at different locations and at different times, but this does not appear to be the case with breath samples. Due to the small sample size, it is not possible to draw firm conclusions regarding the impact of ambient room air on breath sampling and further analysis is required. It is therefore recommended to sample ambient air in parallel with breathing to allow interrogation of any potential VOC contaminants.