Mass spectrometry for real-time quantitative breath analysis

Clinical applications of volatilomic assays

The study of metabolomics is revealing immense potential for diagnosis, therapy monitoring, and understanding of pathogenesis processes. Volatilomics is a subcategory of metabolomics interested in the detection of molecules that are small enough to be released in the gas phase. Volatile compounds produced by cellular processes are released into the blood and lymph, and can reach the external environment through different pathways, such as the blood-air interface in the lung that are detected in breath, or the blood-water interface in the kidney that leads to volatile compounds detected in urine. Besides breath and urine, additional sources of volatile compounds such as saliva, blood, feces, and skin are available. Volatilomics traces its roots back over fifty years to the pioneering investigations in the 1970s. Despite extensive research, the field remains in its infancy, hindered by a lack of standardization despite ample experimental evidence. The proliferation of analytical instrumentations, sample preparations and methods of volatilome sampling still make it difficult to compare results from different studies and to establish a common standard approach to volatilomics. This review aims to provide an overview of volatilomics' diagnostic potential, focusing on two key technical aspects: sampling and analysis. Sampling poses a challenge due to the susceptibility of human samples to contamination and confounding factors from various sources like the environment and lifestyle. The discussion then delves into targeted and untargeted approaches in volatilomics. Some case studies are presented to exemplify the results obtained so far. Finally, the review concludes with a discussion on the necessary steps to fully integrate volatilomics into clinical practice.

Upregulation of key factors of viral entry of corona- and influenza viruses upon TLR3-signaling in cells from the respiratory tract and clinical treatment options by 1,8-Cineol

At the end of the 2019 coronavirus pandemic (COVID-19), highly contagious variants of coronaviruses had emerged. Together with influenza viruses, different variants of the coronavirus currently cause most colds and require appropriate drug treatment. We have investigated the expression of important factors for the replication of these viruses, namely transmembrane protease serine subtype 2 (TMPRSS2), neuropilin1 (NRP1), and angiotensin converting enzyme 2 (ACE2) or tumor necrosis factor-α (TNF-α) after toll like receptor-3 (TLR-3) stimulation using RT-qPCR and flow cytometry (FC) analysis. As model served primary fibroblasts derived from the lung and nasal cavity, as well as epidermal stem cells and fully matured respiratory epithelium. The stimulated cell cultures were treated with pharmaceuticals (Dexamethasone and Enzalutamide) and the outcome was compared with the phytomedicine 1,8-Cineol. The stimulation of TLR3 is sufficient to induce the expression of exactly those targets that were highly expressed in the corresponding culture type, specifically ACE2 and TMPRSS2 in respiratory epithelial stem cells and NRP1 in fibroblast cells. It seems this self-perpetuating cycle of infection-driven upregulation of key viral replication factors by the innate immune system represents an evolutionary advantage for viruses using these transcripts as viral replication factors. Likewise, to the standard pharmaceuticals with proven clinical efficiency, 1,8-Cineol was able to disrupt this self-perpetuating cycle. Considering the minor side effects and negligible pharmacological interactions with other drugs, it is conceivable that an adjuvant or combinatorial therapy with 1,8-Cineol for respiratory diseases caused by corona- or influenza viruses would be beneficial.

Chemical Analysis of Exhaled Vape Emissions: Unraveling the Complexities of Humectant Fragmentation in a Human Trial Study

Electronic cigarette smoking (or vaping) is on the rise, presenting questions about the effects of secondhand exposure. The chemical composition of vape emissions was examined in the exhaled breath of eight human volunteers with the high chemical specificity of complementary online and offline techniques. Our study is the first to take multiple exhaled puff measurements from human participants and compare volatile organic compound (VOC) concentrations between two commonly used methods, proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and gas chromatography (GC). Five flavor profile groups were selected for this study, but flavor compounds were not observed as the main contributors to the PTR-ToF-MS signal. Instead, the PTR-ToF-MS mass spectra were overwhelmed by e-liquid thermal decomposition and fragmentation products, which masked other observations regarding flavorings and other potentially toxic species associated with secondhand vape exposure. Compared to the PTR-ToF-MS, GC measurements reported significantly different VOC concentrations, usually below those from PTR-ToF-MS. Consequently, PTR-ToF-MS mass spectra should be interpreted with caution when reporting quantitative results in vaping studies, such as doses of inhaled VOCs. Nevertheless, the online PTR-ToF-MS analysis can provide valuable qualitative information by comparing relative VOCs in back-to-back trials. For example, by comparing the mass spectra of exhaled air with those of direct puffs, we can conclude that harmful VOCs present in the vape emissions are largely absorbed by the participants, including large fractions of nicotine.

Determination of the two-compartment model parameters of exhaled HCN by fast negative photoionization mass spectrometry

Breath exhaled hydrogen cyanide (HCN) has been identified to be associated with several respiratory diseases. Accurately distinguishing the concentration and release rate of different HCN sources is of great value in clinical research. However, there are still significant challenges due to the high adsorption and low concentration characteristics of exhaled HCN. In this study, a two-compartment kinetic model method based on negative photoionization mass spectrometry was developed to simultaneously determine the kinetic parameters including concentrations and release rates in the airways and alveoli. The influences of the sampling line diameter, length, and temperature on the response time of the sampling system were studied and optimized, achieving a response time of 0.2 s. The negative influence of oral cavity-released HCN was reduced by employing a strategy based on anatomical lung volume calculation. The calibration for HCN in the dynamic range of 0.5-100 ppbv and limit of detection (LOD) at 0.3 ppbv were achieved. Subsequently, the experiments of smoking, short-term passive smoking, and intake of bitter almonds were performed to examine the influences of endogenous and exogenous factors on the dynamic parameters of the model method. The results indicate that compared with steady-state concentration measurements, the kinetic parameters obtained using this model method can accurately and significantly reflect the changes in different HCN sources, highlighting its potential for HCN-related disease research.

Non-destructive egg breed separation using advanced VOC analytical techniques HSSE-GC-MS, PTR-TOF-MS, and SIFT-MS: Assessment of performance and systems' complementarity

Over the past decade, advanced analytical techniques have been utilized to examine volatile organic compounds (VOCs) in eggs. These VOCs offer valuable insights into factors such as freshness, fertility, the presence of cracks, embryo sex, and breed. In our study, we assessed three mass spectrometry-based systems (headspace sorptive extraction gas chromatography-mass spectrometry; HSSE-GC-MS, proton transfer reaction time-of-flight-mass spectrometry; PTR-TOF-MS; and selected ion flow tube mass spectrometry; SIFT-MS) to analyze and identify VOCs present in intact hatching eggs from three distinct breeds (Dekalb white layer, Shaver brown layer, and Ross 308 broiler). The eggs were sampled on incubation days 2 and 8, to identify VOCs that distinguish breeds irrespective of incubation day. VOC measurements were conducted on 15 eggs per breed by placing them together with PDMS-coated stir bars inside inert Teflon® air sampling bags. After an accumulation period of 2 h, the headspace was analyzed using PTR-TOF-MS and SIFT-MS, while the VOCs adsorbed onto the stir bars were analyzed using GC-MS for additional compound identification. Partial least squares discriminant analysis (PLS-DA) models were constructed for breed differentiation, and variable selection was performed. As a result, 111 VOCs were identified using HSSE-GC-MS, with alcohols and esters being the most abundant. The PLS-DA models demonstrated the efficacy of breed discrimination, with the HSSE-GC-MS and the PTR-TOF-MS exhibiting the highest balanced accuracy of 95.5 % using a reduced set of 11 VOCs and 5 product ions, respectively. The SIFT-MS model had a balanced accuracy of 92.8 % with a reduced set of 11 product ions. Furthermore, complementarity was observed between HSSE-GC-MS, which primarily selected higher molecular weight VOCs, and PTR-TOF-MS and SIFT-MS. A higher correlation was found for compound abundances between the HSSE-GC-MS and the PTR-TOF-MS relative to the SIFT-MS, indicating that the PTR-TOF-MS was better suited to quantify specific compounds identified by the HSSE-GC-MS. Finally, the findings support the presence of VOCs originating from both synthetic and natural sources, highlighting the ability of the VOC analysis systems to non-destructively perform quality control and reveal differences in management practices or biological information encoded in eggs.

Preservation of exhaled breath samples for analysis by off-line SESI-HRMS: proof-of-concept study

Secondary electrospray ionization-high resolution mass spectrometry (SESI-HRMS) is an established technique in the field of breath analysis characterized by its short analysis time, as well as high levels of sensitivity and selectivity. Traditionally, SESI-HRMS has been used for real-time breath analysis, which requires subjects to be at the location of the analytical platform. Therefore, it limits the possibilities for an introduction of this methodology in day-to-day clinical practice. However, recent methodological developments have shown feasibility on the remote sampling of exhaled breath in Nalophan® bags prior to measurement using SESI-HRMS. To further explore the range of applications of this method, we conducted a proof-of-concept study to assess the impact of the storage time of exhaled breath in Nalophan® bags at different temperatures (room temperature and dry ice) on the relative intensities of the compounds. In addition, we performed a detailed study of the storage effect of 27 aldehydes related to oxidative stress. After 2 h of storage, the mean of intensity of allm/zsignals relative to the samples analyzed without prior storage remained above 80% at both room temperature and dry ice. For the 27 aldehydes, the mean relative intensity losses were lower than 20% at 24 h of storage, remaining practically stable since the first hour of storage following sample collection. Furthermore, the mean relative intensity of most aldehydes in samples stored at room temperature was higher than those stored in dry ice, which could be related to water vapor condensation issues. These findings indicate that the exhaled breath samples could be preserved for hours with a low percentage of mean relative intensity loss, thereby allowing more flexibility in the logistics of off-line SESI-HRMS studies.

Prediction of systemic free and total valproic acid by off-line analysis of exhaled breath in epileptic children and adolescents

Therapeutic drug monitoring (TDM) of medications with a narrow therapeutic window is a common clinical practice to minimize toxic effects and maximize clinical outcomes. Routine analyses rely on the quantification of systemic blood concentrations of drugs. Alternative matrices such as exhaled breath are appealing because of their inherent non-invasive nature. This is especially the case for pediatric patients. We have recently showcased the possibility of predicting systemic concentrations of valproic acid (VPA), an anti-seizure medication by real-time breath analysis in two real clinical settings. This approach, however, comes with the limitation of the patients having to physically exhale into the mass spectrometer. This restricts the possibility of sampling from patients not capable or available to exhale into the mass spectrometer located on the hospital premises. In this work, we developed an alternative method to overcome this limitation by collecting the breath samples in customized bags and subsequently analyzing them by secondary electrospray ionization coupled to high-resolution mass spectrometry (SESI-HRMS). A total ofn= 40 patients (mean ± SD, 11.5 ± 3.5 y.o.) diagnosed with epilepsy and taking VPA were included in this study. The patients underwent three measurements: (i) serum concentrations of total and free VPA, (ii) real-time breath analysis and (iii) off-line analysis of exhaled breath collected in bags. The agreement between the real-time and the off-line breath analysis methods was evaluated using Lin's concordance correlation coefficient (CCC). CCC was computed for ten mass spectral predictors of VPA concentrations. Lin's CCC was >0.6 for all VPA-associated features, except for two low-signal intensity isotopic peaks. Finally, free and total serum VPA concentrations were predicted by cross validating the off-line data set. Support vector machine algorithms provided the most accurate predictions with a root mean square error of cross validation of 29.0 ± 7.4 mg l-1and 3.9 ± 1.4 mg l-1for total and free VPA (mean ± SD), respectively. As a secondary analysis, we explored whether exhaled metabolites previously associated with side-effects and response to medication could be rendered by the off-line analysis method. We found that five features associated with side effects showed a CCC > 0.6, whereas none of the drug response-associated peaks reached this cut-off. We conclude that the clinically relevant free fraction of VPA can be predicted by this combination of off-line breath collection with rapid SESI-HRMS analysis. This opens new possibilities for breath based TDM in clinical settings.

Breath analysis by ultra-sensitive broadband laser spectroscopy detects SARS-CoV-2 infection

Rapid testing is essential to fighting pandemics such as coronavirus disease 2019 (COVID-19), the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Exhaled human breath contains multiple volatile molecules providing powerful potential for non-invasive diagnosis of diverse medical conditions. We investigated breath detection of SARS-CoV-2 infection using cavity-enhanced direct frequency comb spectroscopy (CE-DFCS), a state-of-the-art laser spectroscopic technique capable of a real-time massive collection of broadband molecular absorption features at ro-vibrational quantum state resolution and at parts-per-trillion volume detection sensitivity. Using a total of 170 individual breath samples (83 positive and 87 negative with SARS-CoV-2 based on reverse transcription polymerase chain reaction tests), we report excellent discrimination capability for SARS-CoV-2 infection with an area under the receiver-operating-characteristics curve of 0.849(4). Our results support the development of CE-DFCS as an alternative, rapid, non-invasive test for COVID-19 and highlight its remarkable potential for optical diagnoses of diverse biological conditions and disease states.

Assessment of an e-nose performance for the detection of COVID-19 specific biomarkers

Early, rapid and non-invasive diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is needed for the prevention and control of coronavirus disease 2019 (COVID-19). COVID-19 mainly affects the respiratory tract and lungs. Therefore, analysis of exhaled breath could be an alternative scalable method for reliable SARS-CoV-2 screening. In the current study, an experimental protocol using an electronic-nose ('e-nose') for attempting to identify a specific respiratory imprint in COVID-19 patients was optimized. Thus the analytical performances of the Cyranose^®, a commercial e-nose device, were characterized under various controlled conditions. In addition, the effect of various experimental conditions on its sensor array response was assessed, including relative humidity, sampling time and flow rate, aiming to select the optimal parameters. A statistical data analysis was applied to e-nose sensor response using common statistical analysis algorithms in an attempt to demonstrate the possibility to detect the presence of low concentrations of spiked acetone and nonanal in the breath samples of a healthy volunteer. Cyranose^®reveals a possible detection of low concentrations of these two compounds, in particular of 25 ppm nonanal, a possible marker of SARS-CoV-2 in the breath.

Recent developments and applications of selected ion flow tube mass spectrometry (SIFT-MS)

Selected ion flow tube mass spectrometry (SIFT-MS) is now recognized as the most versatile analytical technique for the identification and quantification of trace gases down to the parts-per-trillion by volume, pptv, range. This statement is supported by the wide reach of its applications, from real-time analysis, obviating sample collection of very humid exhaled breath, to its adoption in industrial scenarios for air quality monitoring. This review touches on the recent extensions to the underpinning ion chemistry kinetics library and the alternative challenge of using nitrogen carrier gas instead of helium. The addition of reagent anions in the Voice200 series of SIFT-MS instruments has enhanced the analytical capability, thus allowing analyses of volatile trace compounds in humid air that cannot be analyzed using reagent cations alone, as clarified by outlining the anion chemistry involved. Case studies are reviewed of breath analysis and bacterial culture volatile organic compound (VOC), emissions, environmental applications such as air, water, and soil analysis, workplace safety such as transport container fumigants, airborne contamination in semiconductor fabrication, food flavor and spoilage, drugs contamination and VOC emissions from packaging to demonstrate the stated qualities and uniqueness of the new generation SIFT-MS instrumentation. Finally, some advancements that can be made to improve the analytical capability and reach of SIFT-MS are mentioned.

Development and validation of a screening model for lung cancer using machine learning: A large-scale, multi-center study of biomarkers in breath

Objectives

Lung cancer (LC) is the largest single cause of death from cancer worldwide, and the lack of effective screening methods for early detection currently results in unsatisfactory curative treatments. We herein aimed to use breath analysis, a noninvasive and very simple method, to identify and validate biomarkers in breath for the screening of lung cancer.

Materials and methods

We enrolled a total of 2308 participants from two centers for online breath analyses using proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS). The derivation cohort included 1007 patients with primary LC and 1036 healthy controls, and the external validation cohort included 158 LC patients and 107 healthy controls. We used eXtreme Gradient Boosting (XGBoost) to create a panel of predictive features and derived a prediction model to identify LC. The optimal number of features was determined by the greatest area under the receiver‐operating characteristic (ROC) curve (AUC).

Results

Six features were defined as a breath-biomarkers panel for the detection of LC. In the training dataset, the model had an AUC of 0.963 (95% CI, 0.941–0.982), and a sensitivity of 87.1% and specificity of 93.5% at a positivity threshold of 0.5. Our model was tested on the independent validation dataset and achieved an AUC of 0.771 (0.718–0.823), and sensitivity of 67.7% and specificity of 73.0%.

Conclusion

Our results suggested that breath analysis may serve as a valid method in screening lung cancer in a borderline population prior to hospital visits. Although our breath-biomarker panel is noninvasive, quick, and simple to use, it will require further calibration and validation in a prospective study within a primary care setting.

Analysis of volatile organic compounds from deep airway in the lung through intubation sampling

Exhaled volatile organic compounds (VOCs) have been widely applied for the study of disease biomarkers. Oral exhalation and nasal exhalation are two of the most common sampling methods. However, VOCs released from food residues and bacteria in the mouth or upper respiratory tract were also sampled and usually mistaken as that produced from body metabolism. In this study, exhalation from deep airway was first directly collected through intubation sampling and analyzed. The exhalation samples of 35 subjects were collected through a catheter, which was inserted into the trachea or bronchus through the mouth and upper respiratory tract. Then, the VOCs in these samples were detected by proton transfer reaction mass spectrometry (PTR-MS). In addition, fast gas chromatography proton transfer reaction mass spectrometry (FGC-PTR-MS) was used to further determine the VOCs with the same mass-to-charge ratios. The results showed that there was methanol, acetonitrile, ethanol, methyl mercaptan, acetone, isoprene, and phenol in the deep airway. Compared with that in oral exhalation, ethanol, methyl mercaptan, and phenol had lower concentrations. In detail, the median concentrations of ethanol, methyl mercaptan, and phenol were 7.3, 0.6, and 23.9 ppbv, while those in the oral exhalation were 80.0, 5.1, and 71.3 ppbv, respectively, which meant the three VOCs mainly originated from the food residues and bacteria in the mouth or upper respiratory tract, rather than body metabolism. The research results in our study can provide references for expiratory VOC research based on oral and nasal exhalation samplings, which are more feasible in clinical practice.

The potential of NO+ and O2 +• in switchable reagent ion proton transfer reaction time-of-flight mass spectrometry

Selected ion flow tube mass spectrometry (SIFT-MS) and proton transfer reaction mass spectrometry with switchable reagent ion capability (PTR+SRI-MS) are analytical techniques for real-time qualification and quantification of compounds in gas samples with trace level concentrations. In the detection process, neutral compounds-mainly volatile organic compounds-are ionized via chemical ionization with ionic reagents or primary ions. The most common reagent ions are H₃ O⁺ , NO⁺ and O₂ ^+• . While ionization with H₃ O⁺ occurs by means of proton transfer, the ionization via NO⁺ and O₂ ^+• offers a larger variety on ionization pathways, as charge transfer, hydride abstraction and so on are possible. The distribution of the reactant into various reaction channels depends not only on the usage of either NO⁺ or O₂ ^+• , but also on the class of analyte compounds. Furthermore, the choice of the reaction conditions as well as the choice of either SIFT-MS or PTR+SRI-MS might have a large impact on the resulting products. Therefore, an overview of both NO⁺ and O₂ ^+• as reagent ions is given, showing differences between SIFT-MS and PTR+SRI-MS as used analytical methods revealing the potential how the knowledge obtained with H₃ O⁺ for different classes of compounds can be extended with the usage of NO⁺ and O₂ ^+• .

Inhalation of VOCs from facial moisturizers and the influence of dose proximity

Volatile organic compound (VOC) emissions from personal care products (PCPs) contribute to poor indoor air quality. Exposure to indoor VOCs is typically determined through ambient concentration measurements; however, for some PCPs the proximity of use to the nose and mouth may lead to disproportionately large inhaled doses. In this paper, we quantify emission factors for six common PCP ingredient VOCs (ethanol, 2-propanol, benzyl alcohol, 1,3-butanediol, t-butyl alcohol, and the grouping of monoterpenes as limonene) from 16 facial day-moisturizers using headspace analysis and selected ion flow-tube mass spectrometry. A wide range of emissions rates were observed across the range of products tested (e.g., ethanol 3.3-6.9 × 10²  µg s^-1  g_[product]^-1 , limonene 1.3 × 10^-1 -4.1 × 10^-1  µg s^-1  g_[product]^-1 ). We use a mannequin head with reconstructed nose and mouth airways to sample VOCs from facial application at typical respiration volumes. A single facial application of moisturizer can lead to a much larger inhaled VOC dose than would be inhaled from typical indoor ambient air over 24 h (e.g., limonene up to ~×16 greater via facial application, ethanol up to ~×300). Emissions from facially applied PCPs typically decayed to background concentrations over periods ranging from 5 to 150 min.

Point-of-care detection of sevoflurane anesthetics in exhaled breath using a miniature TOFMS for diagnosis of postoperative agitation symptoms in children

A miniature TOFMS with MEPEI has been developed for POC diagnosis of postoperative agitation symptoms, and can analyze sevoflurane by direct sampling. The risk is high when the sevoflurane in the exhaled breath is higher than 500 ppmv.

A Literature Review and Framework Proposal for Halitosis Assessment in Cigarette Smokers and Alternative Nicotine-Delivery Products Users

Halitosis is a health condition which counts cigarette smoking (CS) among its major risk factors. Cigarette smoke can cause an imbalance in the oral bacterial community, leading to several oral diseases and conditions, including intraoral halitosis. Although the best approach to decrease smoking-related health risks is quitting smoking, this is not feasible for many smokers. Switching to potentially reduced-risk products, like electronic vapor products (EVP) or heated tobacco products (HTP), may help improve the conditions associated with CS. To date, there have been few systematic studies on the effects of CS on halitosis and none have assessed the effects of EVP and HTP use. Self-assessment studies have shown large limitations owing to the lack of reliability in the participants' judgment. This has compelled the scientific community to develop a strategy for meaningful assessment of these new products in comparison with cigarettes. Here, we compiled a review of the existing literature on CS and halitosis and propose a 3-layer approach that combines the use of the most advanced breath analysis techniques and multi-omics analysis to define the interactions between oral bacterial species and their role in halitosis both in vitro and in vivo. Such an approach will allow us to compare the effects of different nicotine-delivery products on oral bacteria and quantify their impact on halitosis. Defining the impact of alternative nicotine-delivery products on intraoral halitosis and its associated bacteria will help the scientific community advance a step further toward understanding the safety of these products and their potentiall risks for consumers.

Hyphenated Mass Spectrometry versus Real-Time Mass Spectrometry Techniques for the Detection of Volatile Compounds from the Human Body

Mass spectrometry (MS) is an analytical technique that can be used for various applications in a number of scientific areas including environmental, security, forensic science, space exploration, agri-food, and numerous others. MS is also continuing to offer new insights into the proteomic and metabolomic fields. MS techniques are frequently used for the analysis of volatile compounds (VCs). The detection of VCs from human samples has the potential to aid in the diagnosis of diseases, in monitoring drug metabolites, and in providing insight into metabolic processes. The broad usage of MS has resulted in numerous variations of the technique being developed over the years, which can be divided into hyphenated and real-time MS techniques. Hyphenated chromatographic techniques coupled with MS offer unparalleled qualitative analysis and high accuracy and sensitivity, even when analysing complex matrices (breath, urine, stool, etc.). However, these benefits are traded for a significantly longer analysis time and a greater need for sample preparation and method development. On the other hand, real-time MS techniques offer highly sensitive quantitative data. Additionally, real-time techniques can provide results in a matter of minutes or even seconds, without altering the sample in any way. However, real-time MS can only offer tentative qualitative data and suffers from molecular weight overlap in complex matrices. This review compares hyphenated and real-time MS methods and provides examples of applications for each technique for the detection of VCs from humans.

Breath volatile organic compound analysis: an emerging method for gastric cancer detection

Gastric cancer is a common malignancy, being the fifth most frequently diagnosed cancer and the fourth leading cause of cancer-related deaths worldwide. Diagnosis of gastric cancer at the early stage is critical to effectively improve the survival rate. However, a substantial proportion of patients with gastric cancer in the early stages lack specific symptoms or are asymptomatic. Moreover, the imaging techniques currently used for gastric cancer screening, such as computed tomography and barium examination, are usually radioactive and have low sensitivity and specificity. Even though endoscopy has high accuracy for gastric cancer screening, its application is limited by the invasiveness of the technique. Breath analysis is an economic, effective, easy to perform, non-invasive detection method, and has no undesirable side effects on subjects. Extensive worldwide research has been conducted on breath volatile organic compounds (VOCs), which reveals its prospect as a potential method for gastric cancer detection. Many interesting results have been obtained and innovative methods have been introduced in this subject; hence, an extensive review would be beneficial. By providing a comprehensive list of breath VOCs identified by gastric cancer would promote further research in this field. This review summarizes the commonly used technologies for exhaled breath analysis, focusing on the application of analytical instruments in the detection of breath VOCs in gastric cancers, and the alterations in the profile of breath biomarkers in gastric cancer patients are discussed as well.

Ultrasensitive multispecies spectroscopic breath analysis for real-time health monitoring and diagnostics

Breath analysis enables rapid, noninvasive diagnostics, as well as long-term monitoring of human health, through the identification and quantification of exhaled biomarkers. Here, we demonstrate the remarkable capabilities of mid-infrared (mid-IR) cavity-enhanced direct-frequency comb spectroscopy (CE-DFCS) applied to breath analysis. We simultaneously detect and monitor as a function of time four breath biomarkers-[Formula: see text]OH, [Formula: see text], [Formula: see text]O, and HDO-as well as illustrate the feasibility of detecting at least six more ([Formula: see text]CO, [Formula: see text], OCS, [Formula: see text], [Formula: see text], and [Formula: see text]) without modifications to the experimental apparatus. We achieve ultrahigh detection sensitivity at the parts-per-trillion level. This is made possible by the combination of the broadband spectral coverage of a frequency comb, the high spectral resolution afforded by the individual comb teeth, and the sensitivity enhancement resulting from a high-finesse cavity. Exploiting recent advances in frequency comb, optical coating, and photodetector technologies, we can access a large variety of biomarkers with strong carbon-hydrogen-bond spectral signatures in the mid-IR.

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

A 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, thePeppermint Experimentinvolves the targeted analysis in exhaled breath of volatile constituents of peppermint oil after ingestion of the encapsulated oil. Data from thePeppermint Experimentperformed 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- andβ-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.

The "olfactory fingerprint": can diagnostics be improved by combining canine and digital noses?

A sniffer (detecting) dog is conventionally defined as an animal trained to use its olfactory perceptions for detecting a vast array of substances, mostly volatile organic compounds (VOCs), including those exceptionally or exclusively generated in humans bearing specific pathologies. Such an extraordinary sniffing performance translates into the capability of detecting compounds close to the femtomolar level, with performance comparable to that of current mass spectrometry-based laboratory applications. Not only can dogs accurately detect "abnormal volatilomes" reflecting something wrong happening to their owners, but they can also perceive visual, vocal and behavioral signals, which altogether would contribute to raise their alertness. Although it seems reasonable to conclude that sniffer dogs could never be considered absolutely "diagnostic" for a given disorder, several lines of evidence attest that they may serve as efficient screening aids for many pathological conditions affecting their human companions. Favorable results have been obtained in trials on cancers, diabetes, seizures, narcolepsy and migraine, whilst interesting evidence is also emerging on the capability of early and accurately identifying patients with infectious diseases. This would lead the way to proposing an "olfactory fingerprint" loop, where evidence that dogs can identify the presence of human pathologies provides implicit proof of the existence of disease-specific volatilomes, which can be studied for developing laboratory techniques. Contextually, the evidence that specific pathologies are associated with abnormal VOC generation may serve as reliable basis for training dogs to detect these compounds, even (or especially) in patients at an asymptomatic phase.

Selected ion flow tube mass spectrometry for targeted analysis of volatile organic compounds in human breath

The analysis of volatile organic compounds (VOCs) within breath for noninvasive disease detection and monitoring is an emergent research field that has the potential to reshape current clinical practice. However, adoption of breath testing has been limited by a lack of standardization. This protocol provides a comprehensive workflow for online and offline breath analysis using selected ion flow tube mass spectrometry (SIFT-MS). Following the suggested protocol, 50 human breath samples can be analyzed and interpreted in <3 h. Key advantages of SIFT-MS are exploited, including the acquisition of real-time results and direct compound quantification without need for calibration curves. The protocol includes details of methods developed for targeted analysis of disease-specific VOCs, specifically short-chain fatty acids, aldehydes, phenols, alcohols and alkanes. A procedure to make custom breath collection bags is also described. This standardized protocol for VOC analysis using SIFT-MS is intended to provide a basis for wider application and the use of breath analysis in clinical studies.

Pursuing breath research in unprecedented circumstances-report from the Breath Biopsy Conference 2020

The global outbreak of Sars-CoV-2 commencing early in 2020 had a dramatic impact on breath research, imposing abrupt restrictions but also presenting unforeseen opportunities. Taking place against the background of the COVID-19 pandemic, the 2020 Breath Biopsy Conference provided the breath research community with a platform to showcase and discuss the latest findings, including COVID-19 related research. As with most conferences under the present circumstance, it differed from its predecessor meetings by shifting to a virtual format, but retained its broad scope and interactive nature. The conference centred on four key themes, featuring applications of volatile organic compounds, breath biomarkers for liver disease, study design and data analytics, and, notably this year, breath-based endeavours to detect COVID-19 infection. This meeting report summarizes the events of the conference and spotlights selected contributions.

Cross Platform Analysis of Volatile Organic Compounds Using Selected Ion Flow Tube and Proton-Transfer-Reaction Mass Spectrometry

Volatile breath metabolites serve as potential disease biomarkers. Online mass spectrometry (MS) presents real-time quantification of breath volatile organic compounds (VOCs). The study aims to assess the relationship between two online analytical mass spectrometry techniques in the quantification of target breath metabolites: selected ion flow tube mass spectrometry (SIFT-MS) and proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS). The two following techniques were employed: (i) direct injection with bag sampling using SIFT-MS and PTR-ToF-MS and (ii) direct injection and thermal desorption (TD) tube comparison using PTR-ToF-MS. The concentration of abundant breath metabolites, acetone and isoprene, demonstrated a strong positive linear correlation between both mass spectrometry techniques (r = 0.97, r = 0.89, respectively; p < 0.001) and between direct injection and TD tube (r = 0.97, r = 0.92, respectively; p < 0.001) breath sampling techniques. This was reflected for the majority of short chain fatty acids and alcohols tested (r > 0.80, p < 0.001). Analyte concentrations were notably higher with the direct injection of a sampling bag compared to the TD method. All metabolites produced a high degree of agreement in the detection range of VOCs between SIFT-MS and PTR-ToF-MS, with the majority of compounds falling within 95% of the limits of agreement with Bland-Altman analysis. The cross platform analysis of exhaled breath demonstrates strong positive correlation coefficients, linear regression, and agreement in target metabolite detection rates between both breath sampling techniques. The study demonstrates the transferability of using data outputs between SIFT-MS and PTR-ToF-MS. It supports the implementation of a TD platform in multi-site studies for breath biomarker research in order to facilitate sample transport between clinics and the laboratory.

Real-time versus thermal desorption selected ion flow tube mass spectrometry for quantification of breath volatiles

RATIONALE

Selected ion flow tube mass spectrometry (SIFT-MS) is versatile, rapidly provides result output and determines a wide range of volatiles, making it suitable for biomedical applications. When direct sampling into the SIFT-MS instrument is impractical, combining thermal desorption (TD) and SIFT-MS might offer a solution as it allows sample storage on sorbent tubes for later analysis. This work compares off-line TD SIFT-MS and real-time SIFT-MS for the quantification of selected breath volatiles.

METHODS

Ten healthy non-smoking individuals provided 60 breath samples per method. For off-line analysis, breath was collected onto sorbent tubes via a breath sampler provided with filtered inspiratory air. After TD, samples were re-collected in Tedlar bags which were then connected to the SIFT-MS instrument. For real-time analysis, breath was sampled directly into the instrument. In both cases the analytical method included a total of 155 product ions, and 14 selected volatiles were quantified. The agreement between the methods was assessed using Pearson correlation coefficients and Bland-Altman plots.

RESULTS

Overall, correlations between real-time and off-line analysis were moderate to very strong (r = 0.43-0.92) depending on the volatile of interest, except for 2,3-butanedione and styrene. The difference between real-time and off-line measured breath concentrations (average bias) ranged between -14.57 and 20.48 ppbv. For acetone and isoprene, it was 251.53 and 31.9 ppbv, respectively.

CONCLUSIONS

Real-time SIFT-MS and off-line TD SIFT-MS for quantification of selected breath volatiles did not show optimal agreement. Analyzing a multitude of analytes in breath via direct exhalation into a SIFT-MS instrument for real-time analysis is challenging. On the other hand, off-line analysis using a breath collection device also has its issues such as possible sample losses due to selective absorption depending on the sorbent used or during desorption and transfer to the instrument. Despite these drawbacks, both methods were moderately well correlated.

Fabric-Phase Sorptive Membrane Array As a Noninvasive In Vivo Sampling Device For Human Exposure To Different Compounds

This study introduces an innovative device for the noninvasive sampling and chromatographic analysis of different compounds present in exhaled breath aerosol (EBA). The new sampling device, especially in light of the recent COVID-19 pandemic that forced many countries to impose mandatory facemasks, allows an easy monitoring of the subject’s exposure to different compounds they may come in contact with, actively or passively. The project combines the advantages of a fabric-phase sorptive membrane (FPSM) as an in vivo sampling device with a validated LC-MS/MS screening procedure able to monitor more than 739 chemicals with an overall analysis time of 18 min. The project involves the noninvasive in vivo sampling of the EBA using an FPSM array inserted inside an FFP2 mask. The study involved 15 healthy volunteers, and no restrictions were imposed during or prior to the sampling process regarding the consumption of drinks, food, or drugs. The FPSM array-LC-MS/MS approach allowed us to effectively exploit the advantages of the two complementary procedures (the convenient sampling by an FPSM array and the rapid analysis by LC-MS/MS), obtaining a powerful and green tool to carry out rapid screening analyses for human exposure to different compounds. The flexible fabric substrate, the sponge-like porous architecture of the high-efficiency sol–gel sorbent coating, the availability of a large cache of sorbent coatings, including polar, nonpolar, mixed mode, and zwitterionic phases, the easy installation into the facemask, and the possibility of sampling without interrupting regular activities provide FPSMs unparalleled advantages over other sampling techniques, and their applications are expected to expand to many other clinical or toxicological studies.

Determination of peppermint compounds in breath by needle trap micro-extraction coupled with gas chromatography-tandem mass spectrometry

Breath analysis is an alternative approach for disease diagnosis and for monitoring therapy. The lack of standardized procedures for collecting and analysing breath samples currently limits its use in clinical practice. In order to overcome this limitation, the "Peppermint Consortium" was established within the breath community to carry out breath wash-out experiments and define reference values for a panel of compounds contained in the peppermint oil capsule. Here, we present a needle trap micro-extraction technique coupled with gas chromatography and tandem mass spectrometry for a rapid and accurate determination of alpha-pinene, beta-pinene, limonene, eucalyptol, menthofuran, menthone, menthol and menthyl acetate in mixed breath samples. Detection limits between 1 and 20 pptv were observed when 25 mL of a humidified standard gas mixture were loaded into a needle trap device at a flow rate of 10 mL/min. Inter- and intra-day precisions were lower than 15%, thus confirming the reliability of the assay. Our procedure was used to analyse breath samples taken from a nominally healthy volunteer who were invited to swallow a 200 mg capsule of peppermint oil. Six samples were collected at various times within six hours of ingestion. Analyte concentrations were not affected by the sampling mode (i.e. mixed vs. end-tidal fraction), whereas respiratory rate and exhalation flow rate values slightly influenced the concentration of the target compounds in breath samples.

Selective detection of complex gas mixtures using point contacts: concept, method and tools

Of all modern nanosensors using the principle of measuring variations in electric conductance, point-contact sensors stand out in having a number of original sensor properties not manifested by their analogues. The nontrivial nature of point-contact sensors is based on the unique properties of Yanson point contacts used as the sensing elements. The quantum properties of Yanson point contacts enable the solution of some of the problems that could not be solved using conventional sensors measuring conductance. In the present paper, we demonstrate this by showing the potential of quantum point-contact sensors to selectively detect components of a gas mixture in real time. To demonstrate the high efficiency of the proposed approach, we analyze the human breath, which is the most complex of the currently known natural gas mixtures with extremely low concentrations of its components. Point-contact sensors allow us to obtain a spectroscopic profile of the mixture. This profile contains information about the complete set of energy interactions occurring in the point contact/breath system when the breath constituents adsorb to and desorb from the surface of the point-contact conduction channel. With this information we can unambiguously characterize the analyzed system, since knowing the energy parameters is key to successfully identifying and modeling the physicochemical properties of various quantum objects. Using the point-contact spectroscopic profile of a complex gas mixture it is possible to get a functional dependence of the concentration of particular breath components on the amplitude of the sensor output signal. To demonstrate the feasibility of the proposed approach, we analyze the point-contact profiles from the breath of several patients and compare them with the concentrations of serotonin and cortisol in the body of each patient. The obtained results demonstrate that the proposed methodology allows one to get an effective calibration function for a non-invasive analysis of the level of serotonin and cortisol in the human body using the point-contact breath test. The present study indicates some necessary prerequisites for the design of fast detection methods using differential sensor analysis in real time, which can be implemented in various areas of science and technology, among which medicine is one of the most important.

Real time analysis of trace volatile organic compounds in ambient air: a comparison between membrane inlet single photon ionization mass spectrometry and proton transfer reaction mass spectrometry

Real-time monitoring of volatile organic compounds (VOCs) is critical for a better understanding of chemical processes in ambient air or making minute-by-minute decisions in emergency situations. Proton transfer reaction mass spectrometry (PTR-MS) is nowadays the most commonly used technique for real-time monitoring of VOCs while membrane single photon ionization mass spectrometry (MI-SPI-MS) is a promising MS technique for online detection of trace VOCs. Here, to evaluate the potential of MI-SPI-MS as a complementary tool to PTR-MS, a comprehensive comparison has been performed between MI-SPI-MS and PTR-MS. By using two sets of standard gas mixtures TO15 and PAMS, SPI-MS shows advantages in the detection of ≥C5 alkanes, aromatics and halogens; especially for aromatics, the LODs can reach the ppt level. PTR-MS has performed better in the detection of alkenes, ketones and aldehydes. For outdoor measurements, a number of VOCs have been detected while using MI-SPI-MS and PTR-MS in parallel. Consistent temporal variations have been observed for toluene, C8-aromatics and C9-aromatics by the two instruments, with a more sensitive response from the MI-SPI-MS. Thus by measuring both standard gas mixture and complex ambient air samples, we have successfully demonstrated that MI-SPI-MS will be a helpful tool to provide important complementary information on aromatics and alkanes in air, and proper application of MI-SPI-MS will benefit the real-time monitoring of trace VOCs in relative fields.

Understanding Gas Phase Ion Chemistry Is the Key to Reliable Selected Ion Flow Tube-Mass Spectrometry Analyses

Ion-molecule reactions (IMR) are at the very core of trace gas analyses in modern chemical ionization (CI) mass spectrometer instruments, which are increasingly being used in diverse areas of research and industry. The focus of this Perspective is on the ion chemistry that underpins gas-phase analytical CI methods. Special attention is given to the soft chemical ionization method known as selected ion flow tube-mass spectrometry (SIFT-MS). The processes involved in the ion chemistry of the reagent cations, H₃O⁺, NO⁺, and O₂^+•, and the anions, O^-•, O₂^-•, OH^-, and NO₂^-, are discussed in some detail. Stressed throughout is that an understanding of these processes is mandatory to obtain reliable analyses of humid gaseous media such as ambient air and exhaled breath. It is indicated that further research is needed to understand the consequences of replacing helium in some situations by the more readily available nitrogen as the carrier gas in SIFT-MS.

Solid-Phase Microextraction Fiber in Face Mask for in Vivo Sampling and Direct Mass Spectrometry Analysis of Exhaled Breath Aerosol

Molecular analysis of exhaled breath aerosol (EBA) with simple procedures represents a key step in clinical and point-of-care applications. Due to the crucial health role, a face mask now is a safety device that helps protect the wearer from breathing in hazardous particles such as bacteria and viruses in the air; thus exhaled breath is also blocked to congregate in the small space inside of the face mask. Therefore, direct sampling and analysis of trace constituents in EBA using a face mask can rapidly provide useful insights into human physiologic and pathological information. Herein, we introduce a simple approach to collect and analyze human EBA by combining a face mask with solid-phase microextraction (SPME) fiber. SPME fiber was inserted into a face mask to form SPME-in-mask that covered nose and mouth for in vivo sampling of EBA, and SPME fiber was then coupled with direct analysis in real-time mass spectrometry (DART-MS) to directly analyze the molecular compositions of EBA under ambient conditions. The applicability of SPME-in-mask was demonstrated by direct analysis of drugs and metabolites in oral and nasal EBA. The unique features of SPME-in-mask were also discussed. Our results showed that this method is enabled to analyze volatile and nonvolatile analytes in EBA and is expected to have a significant impact on human EBA analysis in clinical applications. We also hope this method will inspire biomarker screening of some respiratory diseases that usually required wearing of a face mask in daily life.

Effects of modular ion-funnel technology onto analysis of breath VOCs by means of real-time mass spectrometry

Proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) is a powerful tool for real-time monitoring of trace concentrations of volatile organic compounds (VOCs). The sensitivity of PTR-ToF-MS also depends on the ability to effectively focus and transmit ions from the relatively high-pressure drift tube (DT) to the low-pressure mass analyzer. In the present study, a modular ion-funnel (IF) is placed adjacent to the DT of a PTR-ToF-MS instrument to improve the ion-focusing. IF consists of a series of electrodes with gradually decreasing orifice diameters. Radio frequency (RF) voltage and direct current (DC) electric field are then applied to the electrodes to get the ions focused. We investigated the effect of the RF voltage and DC field on the sensitivity of a pattern of VOCs including hydrocarbons, alcohols, aldehydes, ketones, and aromatic compounds. In a proof-of-concept study, the instrument operating both as normal DT (DC-mode) and at optimal IF conditions (RF-mode) was applied for the breath analysis of 21 healthy human subjects. For the range of investigated VOCs, an improvement of one order of magnitude in sensitivity was observed in RF-mode compared with DC-mode. Limits of detection could be improved by a factor of 2–4 in RF-mode compared with DC-mode. Operating the instrument in RF-mode allowed the detection of more compounds in the exhaled air compared with DC-mode. Incorporation of the IF considerably improved the performance of PTR-ToF-MS allowing the real-time monitoring of a larger number of potential breath biomarkers.

Detection of the effects of triclosan (TCS) on the metabolism of VOCs in HepG2 cells by SPI-TOFMS

Volatile organic compounds (VOCs) emitted by organisms and cell metabolism have demonstrated great physiological and pathological values. At present, there is a great interest in the study of volatile metabolome to determine whether VOCs can serve as potential diagnostic biomarkers. In view of the sensitivity of VOCs to physiological changes, the aim of this study was to investigate alterations in VOC profiles in the in vitro headspace of HepG2 cells after exposure to triclosan (TCS). Since the in vivo biological effects of TCS are clearly defined, several TCS-related VOCs may potentially be traced back to common cellular processes. In this study, HepG2 cells were cultured in TCS-containing medium for 2 h, and the emitted VOCs in the headspace of the culture flask were detected using a single photon ionization time-of-flight mass spectrometry instrument. The control group and the TCS-treated group could be well separated by differential VOC profiles, which were related to the physiological states of the HepG2 cells. Compared to the control group, eleven and ten specific VOCs were identified in the 20 μm and 50 μm TCS-treated groups, respectively. Among them, five specific VOCs (m/z 62, 64, 70, 121 and 146) were commonly observed in these two TCS-treated groups. These results indicate that TCS can cause changes in cellular metabolic VOCs, and different concentrations of TCS lead to different VOCs profiles. Based on the findings of the study, the detection of VOCs in cell metabolism can be used as an auxiliary tool to explore the mechanism of drug action, and also as an exploratory method to determine whether drugs play a role in disease treatment.

Real-time selected ion flow tube mass spectrometry to assess short- and long-term variability in oral and nasal breath

Breath-based non-invasive diagnostics have the potential to provide valuable information about a person's health status. However, they are not yet widely used in clinical practice due to multiple factors causing variability and the lack of standardized procedures. This study focuses on the comparison of oral and nasal breathing, and on the variability of volatile metabolites over the short and long term. Selected ion flow tube mass spectrometry (SIFT-MS) was used for online analysis of selected volatile metabolites in oral and nasal breath of 10 healthy individuals five times in one day (short-term) and six times spread over three weeks (long-term), resulting in nearly 100 breath samplings. Intra-class correlation coefficients (ICCs) were used to assess short- and long-term biological variability. Additionally, the composition of ambient air was analyzed at different samplings. The selected volatiles common in exhaled breath were propanol, 2,3-butanedione, acetaldehyde, acetone, ammonia, dimethyl sulfide, isoprene, pentane, and propanal. Additionally, environmental compounds benzene and styrene were analyzed as well. Volatile metabolite concentrations in ambient air were not correlated with those in exhaled breath and were significantly lower than in breath samples. All volatiles showed significant correlation between oral and nasal breath. Five were significantly higher in oral breath compared to nasal breath, while for acetone, propanal, dimethyl sulfide, and ammonia, concentrations were similar in both matrices. Variability depended on the volatile metabolite. Most physiologically relevant volatiles (acetone, isoprene, propanol, acetaldehyde) showed good to very good biological reproducibility (ICC > 0.61) mainly in oral breath and over a short-term period of one day. Both breathing routes showed relatively similar patterns; however, bigger differences were expected. Therefore, since sampling from the mouth is practically more easy, the latter might be preferred.

Monitoring peppermint washout in the breath metabolome by secondary electrospray ionization-high resolution mass spectrometry

In this study, a secondary electrospray ionization-high resolution mass spectrometer (SESI-HRMS) system was employed to profile the real-time exhaled metabolome of ten subjects who had ingested a peppermint oil capsule. In total, six time points were sampled during the experiment. Using an untargeted way of profiling breath metabolome, 2333 m/z unique metabolite features were determined in positive mode, and 1322 in negative mode. To benchmark the performance of the SESI-HRMS setup, several additional checks were done, including determination of the technical variation, the biological variation of one subject within three days, the variation within a time point, and the variation across all samples, taking all m/z features into account. Reproducibility was good, with the median technical variation being 18% and the median variation within biological replicates being 34%. Both variations were lower than the variation across individuals. Washout profiles of compounds from the peppermint oil, including menthone, limonene, pulegone, menthol and menthofuran were determined in all subjects. Metabolites of the peppermint oil were also determined in breath, for example, cis/trans-carveol, perillic acid and menthol glucuronide. Butyric acid was found to be the major metabolite that reduce the uptake rate of limonene. Pathways related to limonene metabolism were examined, and meaningful pathways were identified from breath metabolomics data acquired by SESI using an untargeted analysis.

Modification of an atmospheric pressure photoionization source for online analysis of exhaled breath coupled with quadrupole time-of-flight mass spectrometry

Breath analysis is a promising method for metabolomics studies and clinical diagnosis, as it enables the observation of metabolites in a convenient and noninvasive way. In this work, an atmospheric pressure photoionization (APPI) source was modified for online analysis of exhaled breath by coupling with quadrupole time-of-flight mass spectrometry (QTOFMS). Three parameters, namely, the capillary voltage, the sampling flow and the curtain gas flow of the APPI source, were optimized. Five healthy volunteers, three males and two females, were enrolled to test the performance of modified APPI-QTOFMS by analyzing their exhaled breath. A total of 21 compounds were tentatively identified, and four metabolites, namely, dimethyl selenoxide, δ-valerolactam, hydroxymandelic acid and palmitic amide were detected in the exhaled breath for the first time. The result shows that modified APPI-QTOFMS can be used for the online study of exhaled breath. Graphical abstract.

Applications of Near Infrared Photoacoustic Spectroscopy for Analysis of Human Respiration: A Review

In this review, applications of near-infrared photoacoustic spectroscopy are presented as an opportunity to evaluate human respiration because the measurement of breath is fast, intact and simple to implement. Recently, analytical methods for measuring biomarkers in exhaled air have been extensively developed. With laser-based photoacoustic spectroscopy, volatile organic compounds can be identified with high sensitivity, at a high rate, and with very good selectivity. The literature review has shown the applicability of near-infrared photoacoustic spectroscopy to one of the problems of the real world, i.e., human health. In addition, the review will consider and explore different breath sampling methods for human respiration analysis.

A review of breath analysis techniques in head and neck cancer

Cancers of the head and neck region are a severely disabling group of diseases with no method for early detection. Analysis of exhaled breath volatile organic compounds shows promise as biomarkers for early detection and disease monitoring. This article reviews breath analysis in the setting of head and neck cancer, with a practical focus on breath sampling techniques, detection technologies and valid data analysis methods. Title and abstract keyword searches were conducted on PubMed and Embase databases to identify English language studies without a time-period limitation. The main inclusion criteria were human studies comparing head and neck cancer patients to healthy controls using exhaled breath analysis. Multiple breath collection techniques, three major detection technologies and multiple data analysis methods were identified. However, the variability in techniques and lack of methodological standardization does not allow for adequate study replication or data pooling. Twenty-two volatile organic compounds identified in five studies have been reported to discriminate head and neck cancer patients from healthy controls. Breath analysis for detection of head and neck cancer shows promise as a non-invasive detection tool. However, methodological standardization is paramount for future research study design to provide the potential for translating these techniques into routine clinical use.

Breathomics and treatable traits for chronic airway diseases

PURPOSE OF REVIEW

The long-term management goals of the inflammatory airway diseases asthma and chronic obstructive pulmonary disease (COPD) are similar and focus on symptom control and reduction of exacerbation frequency and severity. Treatable traits have recently been postulated as a management concept which complements the traditional diagnostic labels 'asthma' and 'COPD', thereby focusing on therapy targeted to a patients' individual disease-associated characteristics. Exhaled volatile organic compounds (VOCs) may be utilized as noninvasive biomarker for disease activity or manifestation in asthma and COPD. In this review, we provide an overview of the current achievements concerning exhaled breath analysis in the field of uncontrolled chronic airways diseases.

RECENT FINDINGS

Monitoring of (airway) inflammation and identification of (molecular) phenotypic characteristics in asthma and COPD through exhaled VOC analysis by either mass spectrometry (MS) based or sensor-driven electronic nose technology (eNose) seems to be feasible, however pending confirmation could hamper the valorization of breathomics into clinical tests.

SUMMARY

Exhaled VOC analysis and the management of asthma and COPD through the concept of pulmonary treatable traits are an interesting match. To develop exhaled breath analysis into an added value for pulmonary treatable traits, multicentre studies are required following international standards for study populations, sampling methods and analytical strategies enabling external validation.

Feasibility of perioperative volatile organic compound breath testing for prediction of paralytic ileus following laparoscopic colorectal resection

BACKGROUND

Despite implementation of enhanced recovery after surgery (ERAS) and laparoscopic techniques, postoperative ileus (POI) remains frequent after colorectal surgery, impacting the patient, their recovery and health-care resources. Presently there are no tests that reliably predict or enable early POI diagnosis. Volatile organic compounds (VC) are products of human and microbiota cellular metabolism and we hypothesised that a detectable alteration occurs in POI.

METHOD

This was a prospective observational study of patients undergoing laparoscopic colorectal resection within an established ERAS programme. Standardized end-expiratory breath sampling was performed on the morning of surgery and on the first three postoperative mornings. The concentrations of VCs commonly found in intestinal gas were analysed using selected ion flow tube mass spectrometry and GastroCH₄ ECK®. Feasibility data, bowel preparation, postoperative oral intake, POI and 30-day morbidity were recorded.

RESULTS

Of the 75 potentially eligible patients, 58 (77%) agreed to participate. Per-protocol breath sampling was successfully completed in 94%. There were no analytical failures. Baseline and postoperative concentrations of VCs were broadly comparable and were not altered by bowel preparation or postoperative oral intake. POI developed in 14 (29%) patients. Preoperative ammonia concentration was higher in patients who developed POI [830 parts per billion (ppb) vs 510 ppb, P = 0.027]. There was an increase in the concentration of acetic acid detected on day 2 in patients who developed POI (99 ppb vs 171 ppb, P = 0.021).

CONCLUSION

Repeated VC breath sampling and analysis is feasible in the perioperative setting. An elevated ammonia concentration on the morning of surgery may be a potential predictor of POI.

Direct analysis of aldehydes and carboxylic acids in the gas phase by negative ionization selected ion flow tube mass spectrometry: Quantification and modelling of ion-molecule reactions

RATIONALE

The concentrations of aldehydes and volatile fatty acids have to be controlled because of their potential harmfulness in indoor air or relationship with the organoleptic properties of agri-food products. Although several specific analytical methods are currently used, the simultaneous analysis of these compounds in a complex matrix remains a challenge. The combination of positive and negative ionization selected ion flow tube mass spectrometry (SIFT-MS) allows the accurate, sensitive and high-frequency analysis of complex gas mixtures of these compounds.

METHODS

The ion-molecule reactions of negative precursor ions (OH^- , O^•- , O₂ ^•- , NO₂ ^- and NO₃ ^- ) with five aldehydes and four carboxylic acids were investigated in order to provide product ions and rate constants for the quantification of these compounds by negative ion SIFT-MS. The results were compared with those obtained by conventional analysis methods and/or with already implemented SIFT-MS positive ionization methods. The modelling of hydroxide ion (OH^- )/molecule reaction paths by ab-initio calculation allowed a better understanding of these gas-phase reactions.

RESULTS

Deprotonation systematically occurs by reaction between negative ions and aldehydes or acids, leading to the formation of [M - H]^- primary ions. Ab-initio calculations demonstrated the α-CH deprotonation of aldehydes and the acidic proton abstraction for fatty acids. For aldehydes, the presence of water in the flow tube leads to the formation of hydrated ions, [M - H]^- .H₂ O. With the NO₂ ^- precursor ion, a second reaction channel results in ion-molecule association with the formation of M.NO₂ ^- ions.

CONCLUSIONS

Except for formaldehyde, all the studied compounds can be quantified by negative ion SIFT-MS with significant rate constants. In addition to positive ion SIFT-MS with H₃ O⁺ , O₂ ⁺ and NO⁺ precursor ions, negative ionization with O^•- , O₂ ^•- , OH^- , NO₂ ^- and NO₃ ^- extends the range of analysis of aldehydes and carboxylic acids in air without a preparation or separation step. This methodology was illustrated by the simultaneous quantification in single-scan experiments of seven aldehydes and six carboxylic acids released by building materials.

Non-Invasive Assessment of Metabolic Adaptation in Paediatric Patients Suffering from Type 1 Diabetes Mellitus

An analysis of exhaled volatile organic compounds (VOC) may deliver systemic information quicker than available invasive techniques. Metabolic aberrations in pediatric type 1 diabetes (T1DM) are of high clinical importance and could be addressed via breathomics. Real-time breath analysis was combined with continuous glucose monitoring (CGM) and blood tests in children suffering from T1DM and age-matched healthy controls in a highly standardized setting. CGM and breath-resolved VOC analysis were performed every 5 minutes for 9 hours and blood was sampled at pre-defined time points. Per participant (n = 44) food intake and physical activity were identical and a total of 22 blood samples and 93 minutes of breath samples were investigated. The inter-individual variability of glucose, insulin, glucagon, leptin, and soluble leptin receptor relative to food intake differed distinctly between patients and controls. In T1DM patients, the exhaled amounts of acetone, 2-propanol, and pentanal correlated to glucose concentrations. Of note, the strength of these correlations strongly depended on the interval between food intake and breath sampling. Our data suggests that metabolic adaptation through postprandial hyperglycemia and related oxidative stress is immediately reflected in exhaled breath VOC concentrations. Clinical translations of our findings may enable point-of-care applicability of online breath analysis towards personalized medicine.

Exhaled volatile organic compounds in adult asthma: a systematic review

The search for biomarkers that can guide precision medicine in asthma, particularly those that can be translated to the clinic, has seen recent interest in exhaled volatile organic compounds (VOCs). Given the number of studies reporting "breathomics" findings and its growing integration in clinical trials, we performed a systematic review of the literature to summarise current evidence and understanding of breathomics technology in asthma.A PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses)-oriented systematic search was performed (CRD42017084145) of MEDLINE, Embase and the Cochrane databases to search for any reports that assessed exhaled VOCs in adult asthma patients, using the following terms (asthma AND (volatile organic compounds AND exhaled) OR breathomics).Two authors independently determined the eligibility of 2957 unique records, of which 66 underwent full-text review. Data extraction and risk of bias assessment was performed on the 22 studies deemed to fulfil the search criteria. The studies are described in terms of methodology and the evidence narratively summarised under the following clinical headings: diagnostics, phenotyping, treatment stratification, treatment monitoring and exacerbation prediction/assessment.Our review found that most studies were designed to assess diagnostic potential rather than focus on underlying biology or treatable traits. Results are generally limited by a lack of methodological standardisation and external validation and by insufficiently powered studies, but there is consistency across the literature that exhaled VOCs are sensitive to underlying inflammation. Modern studies are applying robust breath analysis workflows to large multi-centre study designs, which should unlock the full potential of measurement of exhaled volatile organic compounds in airways diseases such as asthma.