Suitability of different polymer bags for storage of volatile sulphur compounds relevant to 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.

An inexpensive UV-LED photoacoustic based real-time sensor-system detecting exhaled trace-acetone

In this research we present a low-cost system for breath acetone analysis based on UV-LED photoacoustic spectroscopy. We considered the end-tidal phase of exhalation, which represents the systemic concentrations of volatile organic compounds (VOCs) - providing clinically relevant information about the human health. This is achieved via the development of a CO2-triggered breath sampling system, which collected alveolar breath over several minutes in sterile and inert containers. A real-time mass spectrometer is coupled to serve as a reference device for calibration measurements and subsequent breath analysis. The new sensor system provided a 3σ detection limit of 8.3 ppbV and an NNEA of 1.4E-9 Wcm-1Hz-0.5. In terms of the performed breath analysis measurements, 12 out of 13 fell within the error margin of the photoacoustic measurement system, demonstrating the reliability of the measurements in the field.

Stability of selected exhaled breath volatiles stored in Tenax®TA adsorbent tubes at -80 °C

Preservation of the breath sample integrity during storage and transport is one of the biggest challenges in off-line exhaled breath gas analysis. In this context, adsorbent tubes are frequently used as storage containers for use with analytical methods employing gas chromatography with mass spectrometric detection. The key objective of this short communication is to provide data on the recovery of selected breath volatiles from Tenax®TA adsorbent tubes that were stored at -80 °C for up to 90 d. For this purpose, an Owlstone Medical's ReCIVA®Breath Sampler was used for exhaled breath collection. The following fifteen compounds, selected to cover a range of chemical properties, were monitored for their stability: isoprene, n-heptane, n-nonane, toluene, p-cymene, allyl methyl sulfide, 1-(methylthio)-propane, 1-(methylthio)-1-propene,α-pinene, DL-limonene,β-pinene,γ-terpinene, 2-pentanone, acetoin and 2,3 butanedione. All compounds, but one (acetoin), were found to be stable during the first 4 weeks of storage (recovery within ± 2 × RSD). Furthermore, n-nonane was stable during the whole of the investigated period.

Benchmarking breath analysis using peppermint approach with gas chromatography ion mobility spectrometer coupled to micro thermal desorber

The Peppermint Initiative, established within the International Association of Breath Research, introduced the peppermint protocol, a breath analysis benchmarking effort designed to address the lack of inter-comparability of outcomes across different breath sampling techniques and analytical platforms. Benchmarking with gas chromatography-ion mobility spectrometry (GC-IMS) using peppermint has been previously reported however, coupling micro-thermal desorption (µTD) to GC-IMS has not yet, been benchmarked for breath analysis. To benchmarkµTD-GC-IMS for breath analysis using the peppermint protocol. Ten healthy participants (4 males and 6 females, aged 20-73 years), were enrolled to give six breath samples into Nalophan bags via a modified peppermint protocol. Breath sampling after peppermint ingestion occurred over 6 h att= 60, 120, 200, 280, and 360 min. The breath samples (120 cm3) were pre-concentrated in theµTD before being transferred into the GC-IMS for detection. Data was processed using VOCal, including background subtractions, peak volume measurements, and room air assessment. During peppermint washout, eucalyptol showed the highest change in concentration levels, followed byα-pinene andβ-pinene. The reproducibility of the technique for breath analysis was demonstrated by constructing logarithmic washout curves, with the average linearity coefficient ofR2= 0.99. The time to baseline (benchmark) value for the eucalyptol washout was 1111 min (95% CI: 529-1693 min), obtained by extrapolating the average logarithmic washout curve. The study demonstrated thatµTD-GC-IMS is reproducible and suitable technique for breath analysis, with benchmark values for eucalyptol comparable to the gold standard GC-MS.

Impact of breath sample collection method and length of storage of breath samples in Tedlar bags on the level of selected volatiles assessed using gas chromatography-ion mobility spectrometry (GC-IMS)

The analysis of volatile organic compounds (VOCs) in exhaled air has attracted the interest of the scientific community because it provides the possibility of monitoring physiological and metabolic processes and non-invasive diagnostics of various diseases. However, this method remains underused in clinical practice as well as in research because of the lack of standardized procedures for the collection, storage and transport of breath samples, which would guarantee good reproducibility and comparability of results. The method of sampling, as well as the storage time of the breath samples in the polymer bags used for sample storage and transport, affect the composition and concentration of VOCs present in the breath samples. The aim of our study was to compare breath samples obtained using two methods with fully disposable equipment: a Haldane sampling tube intended for direct breath collection and breath samples exhaled into a transparent Tedlar bag. The second task was to monitor the stability of selected compounds of real breath samples stored in a Tedlar bag for 6 h. Gas chromatography coupled with ion mobility spectrometry (GC-IMS) implemented in the BreathSpec®device was used to analyse exhaled breath. Our results showed a significant difference in the signal intensity of some volatiles when taking a breath sample with a Haldane tube and a Tedlar bag. Due to its endogenous origin, acetone levels were significantly higher when the Haldane tube sampler was used while elevated levels of 2-propanol and unidentified VOC (designated as VOC 3) in the Tedlar bag samples likely originated from contamination of the Tedlar bags. The VOC stability study revealed compound-specific signal intensity changes of the selected VOCs with storage time in the Tedlar bags, with some volatiles showing increasing signal intensity during storage in Tedlar bags. This limits the use of Tedlar bags only for very limited time and carefully selected purpose. Our results highlight the importance of careful design and implementation of experiments and clinical protocols to obtain relevant and reliable results.

GC-MS-based metabolomics of volatile organic compounds in exhaled breath: applications in health and disease. A review

Exhaled breath analysis, with particular emphasis on volatile organic compounds, represents a growing area of clinical research due to its obvious advantages over other diagnostic tests. Numerous pathologies have been extensively investigated for the identification of specific biomarkers in exhalates through metabolomics. However, the transference of breath tests to clinics remains limited, mainly due to deficiency in methodological standardization. Critical steps include the selection of breath sample types, collection devices, and enrichment techniques. GC-MS is the reference analytical technique for the analysis of volatile organic compounds in exhalates, especially during the biomarker discovery phase in metabolomics. This review comprehensively examines and compares metabolomic studies focusing on cancer, lung diseases, and infectious diseases. In addition to delving into the experimental designs reported, it also provides a critical discussion of the methodological aspects, ranging from the experimental design and sample collection to the identification of potential pathology-specific biomarkers.

Advanced setup for safe breath sampling and patient monitoring under highly infectious conditions in the clinical environment

Being the proximal matrix, breath offers immediate metabolic outlook of respiratory infections. However, high viral load in exhalations imposes higher transmission risk that needs improved methods for safe and repeatable analysis. Here, we have advanced the state-of-the-art methods for real-time and offline mass-spectrometry based analysis of exhaled volatile organic compounds (VOCs) under SARS-CoV-2 and/or similar respiratory conditions. To reduce infection risk, the general experimental setups for direct and offline breath sampling are modified. Certain mainstream and side-stream viral filters are examined for direct and lab-based applications. Confounders/contributions from filters and optimum operational conditions are assessed. We observed immediate effects of infection safety mandates on breath biomarker profiles. Main-stream filters induced physiological and analytical effects. Side-stream filters caused only systematic analytical effects. Observed substance specific effects partly depended on compound's origin and properties, sampling flow and respiratory rate. For offline samples, storage time, -conditions and -temperature were crucial. Our methods provided repeatable conditions for point-of-care and lab-based breath analysis with low risk of disease transmission. Besides breath VOCs profiling in spontaneously breathing subjects at the screening scenario of COVID-19/similar test centres, our methods and protocols are applicable for moderately/severely ill (even mechanically-ventilated) and highly contagious patients at the intensive care.

The Effect of Tedlar Bags on the Composition of Exhaled Human Breath Samples

The PVF Tedlar is widely used for gas collection in clinical diagnostics and environmental research. However, sample collection is frequently associated with the degradation, adsorption, or transformation of sensitive chemicals. Here, we explore to what extent the Tedlar bag collection effects the composition of expired breath samples. Collected breath samples were analyzed using the EESI-MS technique after the storage time of 30 min, 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h, respectively. Our results demonstrated the gradual MS signal decay after 3 h storage. The decay rate of 3 h is about 45% and 6 h is about 88%. Therefore, the Tedlar bag is suggested as a reliable breath holder on the time scale of <3 h.

Differentiation of aspirated nasal air from room air using analysis with a differential mobility spectrometry-based electronic nose: a proof-of-concept study

Over the last few decades, breath analysis using electronic nose (eNose) technology has become a topic of intense research, as it is both non-invasive and painless, and is suitable for point-of-care use. To date, however, only a few studies have examined nasal air. As the air in the oral cavity and the lungs differs from the air in the nasal cavity, it is unknown whether aspirated nasal air could be exploited with eNose technology. Compared to traditional eNoses, differential mobility spectrometry uses an alternating electrical field to discriminate the different molecules of gas mixtures, providing analogous information. This study reports the collection of nasal air by aspiration and the subsequent analysis of the collected air using a differential mobility spectrometer. We collected nasal air from ten volunteers into breath collecting bags and compared them to bags of room air and the air aspirated through the device. Distance and dissimilarity metrics between the sample types were calculated and statistical significance evaluated with Kolmogorov-Smirnov test. After leave-one-day-out cross-validation, a shrinkage linear discriminant classifier was able to correctly classify 100% of the samples. The nasal air differed (p< 0.05) from the other sample types. The results show the feasibility of collecting nasal air by aspiration and subsequent analysis using differential mobility spectrometry, and thus increases the potential of the method to be used in disease detection studies.

A review of environmental odor quantification and qualification methods: The question of objectivity in sensory analysis

For several years, various issues have up surged linked to odor nuisances with impacts on health and economic concerns. As awareness grew, recent development in instrumental techniques and sensorial analysis have emerged offering efficient and complementary approaches regarding environmental odor monitoring and control. While chemical analysis faces several obstacles, the sensory approach can help overcome them. Therefore, this latter may be considered as subjective, putting the reliability of the studies at risk. This paper is a review of the most commonly sensory methodology used for quantitative and qualitative environmental assessment of odor intensity (OI), odor concentration (OC), odor nature (ON) and hedonic tone (HT). For each of these odor dimensions, the assessment techniques are presented and compared: panel characteristics are discussed; laboratory and field studies are considered and the objectivity of the results is debated. For odor quantification, the use of a reference scale for OI assessment offers less subjectivity than other techniques but at the expense of ease-of-use. For OC assessment, the use of dynamic olfactometry was shown to be the least biased. For odor qualification, the ON description was less subjective when a reference-based lexicon was used but at the expense of simplicity, cost, and lesser panel-training requirements. Only when assessing HT was subjectivity an accepted feature because it reflects the impacted communities' acceptance of odorous emissions. For all discussed dimensions, field studies were shown to be the least biased due to the absence of air sampling, except for OC, where the dispersion modeling approach also showed great potential. In conclusion, this paper offers the reader a guide for environmental odor sensory analysis with the capacity to choose among different methods depending on the study nature, expectations, and capacities.

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.

Cheap and easy human breath collection system for trace volatile organic compounds screening using thermal desorption - gas chromatography mass spectrometry

•

By analyzing the VOCs presents in our breath, we could identify if some components should not be present in our bodies, or their concentration is higher or lower than normal.

•

To collect breath samples for VOC analysis, we looked into the current available methodologies and, due to their high prices, tried to develop our own easy and cheap device. A simple single use Minigrip LDPE plastic bag was used in this work and its efficiency and performance were tested.

•

After breath collection, samples were analyzed using Thermal Desorption (TD) system, coupled with Gas Chromatography Mass Spectrometer (GC-MS).

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.

Evaluation of Inoculated Waste Biological Stabilization Degree by Olfactometric Methods

As a result of compounds’ transformation in the waste biostabilization phases, there is an increase in odor nuisance and health problems among people exposed to odorants. Linking the odor concentration to the degree of waste biostabilization may be an important tool for the assessment of individual technological variants of biostabilization. The study aimed to link the odor emissions to the biostabilization degree in individual process variants that differed in the inoculum. The tests were carried out on inoculated windrows on the waste mechanical-bological treatment open site. Odor concentrations were measured during the entire seven-week process of biostabilization (weeks 1–7) and compared with kinetics parameters of organic compounds’ decomposition. The olfactometric tests showed the necessity of using the preparation to reduce the value of odor concentration. Research proved that the decrease of odor concentration values could be useful to indicate the particular phases of biostabilization. Also, the proposed method provides an opportunity to optimize the process concerning the function related to the low degree of odor nuisance of the technologies, including selection of environmentally safe inoculum. This issue has application values that may result in the implementation of new control systems for waste stabilization bioreactors and the evaluation of applied technological solutions.

Breath Analysis: Comparison among Methodological Approaches for Breath Sampling

Despite promising results obtained in the early diagnosis of several pathologies, breath analysis still remains an unused technique in clinical practice due to the lack of breath sampling standardized procedures able to guarantee a good repeatability and comparability of results. The most diffuse on an international scale breath sampling method uses polymeric bags, but, recently, devices named Mistral and ReCIVA, able to directly concentrate volatile organic compounds (VOCs) onto sorbent tubes, have been developed and launched on the market. In order to explore performances of these new automatic devices with respect to sampling in the polymeric bag and to study the differences in VOCs profile when whole or alveolar breath is collected and when pulmonary wash out with clean air is done, a tailored experimental design was developed. Three different breath sampling approaches were compared: (a) whole breath sampling by means of Tedlar bags, (b) the end-tidal breath collection using the Mistral sampler, and (c) the simultaneous collection of the whole and alveolar breath by using the ReCIVA. The obtained results showed that alveolar fraction of breath was relatively less affected by ambient air (AA) contaminants (p-values equal to 0.04 for Mistral and 0.002 for ReCIVA Low) with respect to whole breath (p-values equal to 0.97 for ReCIVA Whole). Compared to Tedlar bags, coherent results were obtained by using Mistral while lower VOCs levels were detected for samples (both breath and AA) collected by ReCIVA, likely due to uncorrected and fluctuating flow rates applied by this device. Finally, the analysis of all data also including data obtained by explorative analysis of the unique lung cancer (LC) breath sample showed that a clean air supply might determine a further confounding factor in breath analysis considering that lung wash-out is species-dependent.

Analytical Tools for Disease Diagnosis in Animals via Fecal Volatilome

Volatilome analysis is growing in attention for the diagnosis of diseases in animals and humans. In particular, volatilome analysis in fecal samples is starting to be proposed as a fast, easy and noninvasive method for disease diagnosis. Volatilome comprises volatile organic compounds (VOCs), which are produced during both physiological and patho-physiological processes. Thus, VOCs from a pathological condition often differ from those of a healthy state and therefore the VOCs profile can be used in the detection of some diseases. Due to their strengths and advantages, feces are currently being used to obtain information related to health status in animals. However, they are complex samples, that can present problems for some analytical techniques and require special consideration in their use and preparation before analysis. This situation demands an effort to clarify which analytic options are currently being used in the research context to analyze the possibilities these offer, with the final objectives of contributing to develop a standardized methodology and to exploit feces potential as a diagnostic matrix. The current work reviews the studies focused on the diagnosis of animal diseases through fecal volatilome in order to evaluate the analytical methods used and their advantages and limitations. The alternatives found in the literature for sampling, storage, sample pretreatment, measurement and data treatment have been summarized, considering all the steps involved in the analytical process.

The Role of Electronic Noses in Phenotyping Patients with Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common progressive disorder of the respiratory system which is currently the third leading cause of death worldwide. Exhaled breath analysis is a non-invasive method to study lung diseases, and electronic noses have been extensively used in breath research. Studies with electronic noses have proved that the pattern of exhaled volatile organic compounds is different in COPD. More recent investigations have reported that electronic noses could potentially distinguish different endotypes (i.e., neutrophilic vs. eosinophilic) and are able to detect microorganisms in the airways responsible for exacerbations. This article will review the published literature on electronic noses and COPD and help in identifying methodological, physiological, and disease-related factors which could affect the results.

Non-invasive cancer detection using volatile biomarkers: Is urine superior to breath?

In recent years numerous reports have highlighted the options of chemical breath analysis with regard to non-invasive cancer detection. Certain volatile organic compounds (VOC) supposedly present in higher amounts or in characteristic patterns have been suggested as potential biomarkers. However, so far no clinical application based on a specific set of compounds appears to exist. Numerous reports on the capability of sniffer dogs and sensor arrays or electronic noses to distinguish breath of cancer patients and healthy controls supports the concept of genuine cancer-related volatile profiles. However, the actual compounds responsible for the scent are completely unknown and there is no correlation with the potential biomarkers suggested on basis of chemical trace analysis. It is outlined that specific features connected with the VOC analysis in breath - namely small concentrations of volatiles, interfering background concentrations, considerable sampling effort and sample instability, impracticability regarding routine application - stand in the way of substantial progress. The underlying chemical-analytical challenge can only be met considering the severe susceptibility of VOC determination to these adverse conditions. Therefore, the attention is drawn to the needs for appropriate quality assurance/quality control as the most important feature for the reliable quantification of volatiles present in trace concentration. Consequently, the advantages of urine as an alternative matrix for volatile biomarker search in the context of diagnosing lung and other cancers are outlined with specific focus on quality assurance and practicability in clinical chemistry. The headspace over urine samples as the VOC source allows adapting gas chromatographical procedures well-established in water analysis. Foremost, the selection of urine over breath as non-invasive matrix should provide considerably more resilience to adverse effects during sampling and analysis. The most important advantage of urine over breath is seen in the option to partition, dispense, mix, spike, store, and thus to dispatch taylor-made urine samples on demand for quality control measures. Although it is still open at this point if cancer diagnosis supported by non-invasively sampled VOC profiles will ultimately reach clinical application the advantages of urine over breath should significantly facilitate urgently required steps beyond the current proof-of-concept stage and towards standardisation.

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.

Volatile compounds released by Nalophan; implications for selected ion flow tube mass spectrometry and other chemical ionisation mass spectrometry analytical methods

Nalophan bags are commonly used to collect breath samples for volatile metabolite analysis. Volatile organic compounds (VOCs) released from the polymer can, however, be mistaken as breath metabolites when analyses are performed by selected ion flow tube mass spectrometry, SIFT-MS, or techniques that depend on a proper understanding of ion chemistry.

METHODS

Three analytical techniques were used to analyse the VOCs released into the nitrogen used to expand Nalophan bags, viz. gas chromatography/mass spectrometry (GC/MS), secondary electrospray ionization mass spectrometry (SESI-MS) and selected ion flow tube mass spectrometry (SIFT-MS). The most significant VOCs were identified and quantified by SIFT-MS as a function of storage time, temperature and humidity.

RESULTS

The consistent results obtained by these three analytical methods identify 1,2-ethanediol (ethylene glycol) and 2-methyl-1,3-dioxolane as the major VOCs released by the Nalophan. Their concentrations are enhanced by increasing the bag storage temperature and time, reaching 170 parts-per-billion by volume (ppbv) for ethylene glycol and 34 ppbv for 2-methyl-1,3-dioxolane in humid nitrogen (absolute humidity of 5%) contained in an 8-L Nalophan bag stored at 37°C for 160 min.

CONCLUSIONS

Using H₃ O⁺ reagent ions for SIFT-MS and SESI-MS analyses, the following analyte ions (m/z values) are affected by the Nalophan impurities: 45, 63, 81, 89 and 99, which can compromise analyses of acetaldehyde, ethylene glycol, monoterpenes, acetoin, butyric acid, hexanal and heptane.

Storage Stability of Volatile Organic Compounds from Petrochemical Plant of China in Different Sample Bags

According to the emission characteristics of volatile organic compounds (VOCs) in the petrochemical plants of China, the storage stability of VOCs for two different bags, polyester aluminum (PEA) and polyvinyl fluoride (PVF), was investigated in this study by comparing the adsorption of gas samples. A series of experiments were carried out to study the impact of different factors of sampling in the petrochemical industry. The results showed that the C2∼C3 substances can be adsorbed by the Tedlar bag, and after being refilled with pure nitrogen, the VOCs adsorbed previously by the bag material can be released. The aromatic hydrocarbon VOCs with larger molecular weight had a relatively lower recovery rate than the smaller molecular weights. And the average recovery of PEA airbags was significantly better than that of PVF airbags for storing stationary VOCs in the refinery of China. More kinds of substances can be detected in the airbags that had been added with helium protective gas, and it had a higher recovery rate for both kinds of simple bags after 24 hours of storage time, which indicated that the airbags without protective gas had adsorbed these substances.

Importance of 2,4,6-Trichloroanisole (TCA) as an odorant in the emissions from anaerobically stabilized dewatered biosolids

Odours from stabilized biosolids after anaerobic digestion of wastewater sludge can cause local community impact. Apart from the well-known odorants such as sulfur compounds, contributions from other volatile organic compounds (VOCs) to nuisance odours is limited. The presence of compounds with low odour detection thresholds (ODTs) at low concentrations, can present challenges for analytical identification. Thirty-six biosolids samples were taken after anaerobic stabilisation and dewatering at a wastewater treatment plant, Sydney, Australia. Biosolid cake samples were stored outside in loosely covered trays under aerobic conditions, however without interactions with soil microorganisms as it would be in reality. All biosolids cake samples were analysed over a period of 35 days. Emissions were collected onto Tenax TA sorbent tubes using a U.S. EPA flux hood method at storage days 1, 3, 7, 10, 14, 21 and 35. Gas chromatography (GC) coupled with mass spectrometer detector (MSD) and an olfactory detection port (ODP) was used to identify a musty/moldy/earthy type odorant in the biosolids emissions as 2,4,6-trichloroanisole (TCA). Measured odour intensities, classified on a scale from 1 to 4, and odour characters were specified by three ODP assessors. TCA was identified in all biosolid cake emissions. The measured odour intensities of the TCA did not significantly alter as the biosolids were aged, however varied between biosolids cakes. Due to its odour intensity, 85% frequency of detection and its low ODT, which is orders of magnitudes lower than sulfur compounds, TCA should be considered as a potential odorant of concern in biosolids emissions.

Odor generation patterns during different operational composting stages of anaerobically digested sewage sludge

This study aimed to evaluate the global patterns of odor generation and odorant composition for different operational stages of anaerobically digested sewage sludge (ADS) composting at pilot scale. To this end, gas emissions were sampled and analyzed during storage, forced aeration treatment (active phase), turning process and curing. For each operational stage, odors were monitored by measuring the odor emission rates (OER in OU_E h^-1 kg^-1ADS) through dynamic olfactometry and computing the odor activity values (OAVs) of compounds quantified by analytical methods (i.e., GC/MS). Ammonia and volatile sulfur compounds (VSCs) were the most abundant air pollutants, representing 55.5% and 20.6% of the cumulative mass emitted, respectively. The first eight days of aerobic treatment and the first turning of the compostable mixture were the critical steps for odor generation with OER ranging from 30 to 317 OU_E h^-1 kg^-1ADS. Particularly, the first turning process was responsible for strong odor episodes that were emitted in a short process time (295 OU_E h^-1 kg^-1ADS). Based on the OAVs approach, dimethyl disulfide, dimethyl sulfide, and methanethiol were the predominant odorants along these early operational stages. Odor potential and composition shifted for the middle and later active phase, second turning, and curing stage where OER fluctuated from 0.18 to 12.6 OU_E h^-1 kg^-1ADS, and hydrogen sulfide showed the most substantial odor contribution. A principal component analysis explaining 77% of the variability in odor concentration and OAVs datasets eased the recognition of these odor patterns.

Comparison of breath sampling methods: a post hoc analysis from observational cohort studies

In this report, we present a post hoc analysis from two observational cohorts, comparing the global breath volatile profile captured when using polymer sampling bags (mixed breath) versus Bio-VOC™ (alveolar breath). The cohorts were originally designed to characterize the breath volatile profiles of Malawian children with and without uncomplicated falciparum malaria. Children aged 3-15 years were recruited from ambulatory pediatric centers in Lilongwe, Malawi. Breath sampling was carried out two months apart (one study using a Bio-VOC™ and the second using sampling bags), and all samples were analyzed by gas chromatography/mass spectrometry. The efficacy of breath collection was assessed by quantifying levels of two high prevalence breath compounds, acetone and isoprene, as well as determining the overall number of breath compounds collected and their abundance. We found that the mean number of volatiles detected using sampling bags was substantially higher than when using the Bio-VOC™ (137 vs. 47). Breath collection by Bio-VOC™ also yielded reduced levels of endogenous breath volatiles, isoprene and acetone, even after breath volume correction. This suggests that the Bio-VOC™ dilutes the volatiles and introduces dead air or ambient air. Our results suggest that sampling bags are better suited for biomarker discovery and untargeted search of volatiles in pediatric populations, as evidenced by superior breath volatile detection.

Chemical and odor characterization of gas emissions released during composting of solid wastes and digestates

Hazardous and odorous gas emissions from composting and methanization plants are an issue of public concern. Odor and chemical monitoring are thus critical steps in providing suitable strategies for air pollution control at waste treatment units. In this study, 141 gas samples were extensively analyzed to characterize the odor and chemical emissions released upon the aerobic treatment of 10 raw substrates and five digestates. For this purpose, agricultural wastes, biowastes, green wastes, sewage sludge, and municipal solid waste (MSW) were composted in 300 L pilots under forced aeration. Gas exhausts were evaluated through dynamic olfactometry and analytical methods (i.e., GC/MS) to determine their odor concentration (OC in OU_E m^-3) and chemical composition. A total of 60 chemical compounds belonging to 9 chemical families were identified and quantified. Terpenes, oxygenated compounds, and ammonia exhibited the largest cumulative mass emission. Odor emission rates (OU_E h^-1) were computed based on OC measurements and related to the initial amount of organic matter composted and the process time to provide odor emission factors (OEFs in OU_E g^-1OM₀). The composting process of solid wastes accounted for OEFs ranging from 65 to 3089 OU_E g^-1OM₀, whereas digestates composting showed a lower odor emission potential with OEF fluctuating from 8.6 to 30.5 OU_E g^-1OM₀. Moreover, chemical concentrations of single compounds were weighted with their corresponding odor detection thresholds (ODTs) to yield odor activities values (OAVs) and odor contribution (PO_i, %). Volatile sulfur compounds were the main odorants (PO_i = 54-99%) regardless of the operational composting conditions or substrate treated. Notably, methanethiol was the leading odorant for 73% of the composting experiments.

Exhaled breath condensate volatilome allows sensitive diagnosis of persistent asthma

BACKGROUND

The diagnosis and phenotyping of paediatric asthma are particularly complex due to the lack of currently available sensitive diagnostic tools. This often results in uncertainties associated with inhaled steroid therapy prescription. Therefore, this study aimed to investigate whether volatile organic compounds measured in exhaled breath condensate can be used as biomarkers for asthma diagnosis in the paediatric population.

METHODS

A total of 64 participants, aged 6-18 years, were recruited on a random basis during visits to an outpatient allergy clinic and to a juvenile football team training session. Lung function, airway reversibility and skin prick tests were performed. Exhaled breath condensate samples were collected, and breathprints were assessed using an electronic nose. Information on medical diagnosis of asthma, rhinitis and atopic dermatitis was retrieved for each participant. A hierarchical cluster model based on the volatilome profiles was then created.

RESULTS

A two-cluster exhaled volatile organic compound-based hierarchical model was able to significantly discriminate individuals with asthma from those without the disease (AUC = 0.81 [0.69-0.93], P < 0.001). Individuals who had persistent asthma and were prescribed corticosteroid therapy by the physician were also significantly distinguished in the model (AUC = 0.81 [0.70-0.92], P < 0.001). Despite being less specific, the method showed higher overall accuracy, sensitivity and AUC values when compared to spirometry with bronchodilation.

CONCLUSIONS

Analysis of the exhaled breath condensate volatilome allowed the distinction of paediatric individuals with a medical diagnosis of asthma, identifying those in need of corticosteroid therapy.

Breath Collection from Children for Disease Biomarker Discovery

Breath collection and analysis can be used to discover volatile biomarkers in a number of infectious and non-infectious diseases, such as malaria, tuberculosis, lung cancer, and liver disease. This protocol describes a reproducible method for sampling breath in children and then stabilizing breath samples for further analysis with gas chromatography-mass spectrometry (GC-MS). The goal of this method is to establish a standardized protocol for the acquisition of breath samples for further chemical analysis, from children aged 4-15 years. First, breath is sampled using a cardboard mouthpiece attached to a 2-way valve, which is connected to a 3 L bag. Breath analytes are then transferred to a thermal desorption tube and stored at 4-5 °C until analysis. This technique has been previously used to capture breath of children with malaria for successful breath biomarker identification. Subsequently, we have successfully applied this technique to additional pediatric cohorts. The advantage of this method is that it requires minimal cooperation on part of the patient (of particular value in pediatric populations), has a short collection period, does not require trained staff, and can be performed with portable equipment in resource-limited field settings.

Breath analysis by two-dimensional gas chromatography with dual flame ionisation and mass spectrometric detection - Method optimisation and integration within a large-scale clinical study

•

New method for the analysis of exhaled breath VOCs by TD-GC × GC-FID/qMS.

•

Optimisation of flow modulation and dual detection alongside clinical requirements.

•

Addresses key challenges of using GC × GC for large-scale breath metabolomics.

Precision medicine has spurred new innovations in molecular pathology leading to recent advances in the analysis of exhaled breath as a non-invasive diagnostic tool. Volatile organic compounds (VOCs) detected in exhaled breath have the potential to reveal a wealth of chemical and metabolomic information. This study describes the development of a method for the analysis of breath, based on automated thermal desorption (TD) combined with flow modulated comprehensive two-dimensional gas chromatography (GC×GC) with dual flame ionisation and quadrupole mass spectrometric detection (FID and qMS). The constrained optimisation and analytical protocol was designed to meet the practical demands of a large-scale multi-site clinical study, while maintaining analytical rigour to produce high fidelity data. The results demonstrate a comprehensive method optimisation for the collection and analysis of breath VOCs by GC×GC, integral to the standardisation and integration of breath analysis within large clinical studies.

Exhaled human breath analysis in active pulmonary tuberculosis diagnostics by comprehensive gas chromatography-mass spectrometry and chemometric techniques

Tuberculosis (TB) is the deadliest infectious disease, and yet accurate diagnostics for the disease are unavailable for many subpopulations. In this study, we investigate the possibility of using human breath for the diagnosis of active TB among TB suspect patients, considering also several risk factors for TB for smokers and those with human immunodeficiency virus (HIV). The analysis of exhaled breath, as an alternative to sputum-dependent tests, has the potential to provide a simple, fast, non-invasive, and readily available diagnostic service that could positively change TB detection. A total of 50 individuals from a clinic in South Africa were included in this pilot study. Human breath has been investigated in the setting of active TB using the thermal desorption-comprehensive two-dimensional gas chromatography-time of flight mass spectrometry methodology and chemometric techniques. From the entire spectrum of volatile metabolites in breath, three machine learning algorithms (support vector machines, partial least squares discriminant analysis, and random forest) to select discriminatory volatile molecules that could potentially be useful for active TB diagnosis were employed. Random forest showed the best overall performance, with sensitivities of 0.82 and 1.00 and specificities of 0.92 and 0.60 in the training and test data respectively. Unsupervised analysis of the compounds implicated by these algorithms suggests that they provide important information to cluster active TB from other patients. These results suggest that developing a non-invasive diagnostic for active TB using patient breath is a potentially rich avenue of research, including among patients with HIV comorbidities.

A Study of Diagnostic Accuracy Using a Chemical Sensor Array and a Machine Learning Technique to Detect Lung Cancer

Lung cancer is the leading cause of cancer death around the world, and lung cancer screening remains challenging. This study aimed to develop a breath test for the detection of lung cancer using a chemical sensor array and a machine learning technique. We conducted a prospective study to enroll lung cancer cases and non-tumour controls between 2016 and 2018 and analysed alveolar air samples using carbon nanotube sensor arrays. A total of 117 cases and 199 controls were enrolled in the study of which 72 subjects were excluded due to having cancer at another site, benign lung tumours, metastatic lung cancer, carcinoma in situ, minimally invasive adenocarcinoma, received chemotherapy or other diseases. Subjects enrolled in 2016 and 2017 were used for the model derivation and internal validation. The model was externally validated in subjects recruited in 2018. The diagnostic accuracy was assessed using the pathological reports as the reference standard. In the external validation, the areas under the receiver operating characteristic curve (AUCs) were 0.91 (95% CI = 0.79–1.00) by linear discriminant analysis and 0.90 (95% CI = 0.80–0.99) by the supportive vector machine technique. The combination of the sensor array technique and machine learning can detect lung cancer with high accuracy.

Key Odorants from Pig Production Based on Improved Measurements of Odor Threshold Values Combining Olfactometry and Proton-Transfer-Reaction Mass Spectrometry (PTR-MS)

Analytical measurements of odorants in combination with odor threshold values is an alternative to sensory measurements that can be used to evaluate abatement technologies for pig production facilities. The purpose of the present study was to estimate odor threshold values for key odorants found in pig house air. A new method was applied where an olfactometer was used to dilute the sample air and the concentrations of odorants presented to the panelists at the dilutions steps were measured by proton-transfer-reaction mass spectrometry (PTR-MS). The results demonstrate that the odor threshold values of acetic acid, butanoic acid, and 4-methylphenol are considerably lower than reported previously, whereas the values of hydrogen sulfide, methanethiol and dimethylsulfide were comparable. Consequently, acetic acid, butanoic acid, and 4-methyl-phenol will have a larger influence on odor from pig production facilities than previously assumed. The results highlight the necessity for directly measuring exposure concentrations when determining odor threshold values.

A comparison of sample preparation methods for extracting volatile organic compounds (VOCs) from equine faeces using HS-SPME

INTRODUCTION

Disturbance to the hindgut microbiota can be detrimental to equine health. Metabolomics provides a robust approach to studying the functional aspect of hindgut microorganisms. Sample preparation is an important step towards achieving optimal results in the later stages of analysis. The preparation of samples is unique depending on the technique employed and the sample matrix to be analysed. Gas chromatography mass spectrometry (GCMS) is one of the most widely used platforms for the study of metabolomics and until now an optimised method has not been developed for equine faeces.

OBJECTIVES

To compare a sample preparation method for extracting volatile organic compounds (VOCs) from equine faeces.

METHODS

Volatile organic compounds were determined by headspace solid phase microextraction gas chromatography mass spectrometry (HS-SPME-GCMS). Factors investigated were the mass of equine faeces, type of SPME fibre coating, vial volume and storage conditions.

RESULTS

The resultant method was unique to those developed for other species. Aliquots of 1000 or 2000 mg in 10 ml or 20 ml SPME headspace were optimal. From those tested, the extraction of VOCs should ideally be performed using a divinylbenzene-carboxen-polydimethysiloxane (DVB-CAR-PDMS) SPME fibre. Storage of faeces for up to 12 months at - 80 °C shared a greater percentage of VOCs with a fresh sample than the equivalent stored at - 20 °C.

CONCLUSIONS

An optimised method for extracting VOCs from equine faeces using HS-SPME-GCMS has been developed and will act as a standard to enable comparisons between studies. This work has also highlighted storage conditions as an important factor to consider in experimental design for faecal metabolomics studies.

Diagnostic accuracy of breath tests for pneumoconiosis using an electronic nose

Breath analyses have attracted substantial attention as screens for occupational environmental lung disease. The objective of this study was to develop breath tests for pneumoconiosis by analysing volatile organic compounds using an electronic nose. A case-control study was designed. We screened 102 subjects from a cohort of stone workers. After excluding three subjects with poorly controlled diabetes mellitus and one subject with asthma, 98 subjects were enrolled, including 34 subjects with pneumoconiosis and 64 healthy controls. We analysed the subjects' breath using an electronic nose with 32 nanocomposite sensors. Data were randomly split into 80% for model building and 20% for validation. Using a linear discriminate analysis, the sensitivity, specificity, accuracy, and area under the receiver operating characteristic curve (AUROC) were 67.9%, 88.0%, 80.8%, and 0.91, respectively, in the training set and 66.7%, 71.4%, 70.0%, and 0.86, respectively, in the test set. In subgroup analysis divided by smoking status, the AUROCs for current smokers, former smokers, and subjects who never smoked were 0.94, 0.93, and 0.99, respectively. In subgroup analysis divided by gender, the AUROCs for males and females were 0.95 and 0.99, respectively. Breath tests may have potential as a screen for pneumoconiosis. A multi-centre study is warranted, and the procedures must be standardized before clinical application.

Oxidative stress in asthmatic and non-asthmatic adolescent swimmers-A breathomics approach

We hypothesize that oxidative stress induced by trichloramine exposure during swimming could be related to etiopathogenesis of asthma among elite swimmers.

AIM

To investigate the effect of a swimming training session on oxidative stress markers of asthmatic compared to non-asthmatic elite swimmers using exhaled breath (EB) metabolomics.

METHODS

Elite swimmers annually screened in our department (n=27) were invited and those who agreed to participate (n=20, of which 9 with asthma) had EB collected (Tedlar^® bags) before and after a swimming training session. SPME fiber (DVB/CAR/PDMS) was used to extract EB metabolites followed by a multidimensional gas chromatography analysis (GC×GC-ToFMS). Dataset comprises eight metabolites end products of lipid peroxidation: five aliphatic alkanes (nonane, 2,2,4,6,6-pentamethylheptane, decane, dodecane, and tetradecane) and three aldehydes (nonanal, decanal, and dodecanal). To assess exercise impact on lipid peroxidation markers, data were analyzed using principle component analysis (PCA), which was run on the original data set and on the data set constructed using differences in the metabolite total areas before and after exercise session.

RESULTS

Heatmap representation revealed that metabolites content decreased after exercise, both for control and asthma groups; however, the greater decrease was observed for controls. Asthmatics and controls did not form separated clusters; however, control swimmers demonstrated a more varied response to the exercise being dispersed along all score plot.

CONCLUSION

In well-trained athletes, swimming is associated with a decrease in oxidative stress markers independently of the presence of asthma, although a more pronounced decrease was seen in controls.

H2S Loss through Nalophan™ Bags: Contributions of Adsorption and Diffusion

Hydrogen-sulfide (H₂S) is a molecule of small dimensions typically present in the odor emissions from different plants. The European Standard EN 13725:2003 set a maximum storage time allowed of 30 hours, during which the sampling bag has to maintain the mixture of odorants with minimal changes. This study investigates the H₂S losses through Nalophan bags and it shows that nonnegligible losses of H₂S can be observed. The percent H₂S loss after 30 hrs with respect to the initial concentration is equal to 33%  ± 3% at a relative humidity of 20% and equal to 22%  ± 1% at a relative humidity of 60%. The average quantity of adsorbed H₂S at 30 h is equal to 2.17 10⁵ g_H2S/g_Nalophan at a storage humidity of 20% and equal to 1.79 10⁵ g_H2S/g_Nalophan at a storage humidity of 60%. The diffusion coefficients of H₂S through Nalophan, for these two humidity conditions tested, are comparable (i.e., 7.5 10⁻¹² m²/sec at 20% humidity and 6.6 10⁻¹² m²/sec at 60% humidity).

Exhaled breath analysis for the early detection of lung cancer: recent developments and future prospects

In lung cancer, the prognosis and treatment options depend directly on tumor size and its spread at the time of diagnosis. There is therefore a constant search for methods that will allow early detection of cancerous lung nodules. With advancing imaging technology and implantation of screening routines in high-risk populations by low-dose computerized tomography, a significant increase in the number of diagnosed small peripheral lesions can be expected. While early detection of small cancerous lesions carries the benefit of wider treatment options and better prognosis, the process of obtaining a biopsy to confirm a cancerous tissue is not free of complications and bears inconveniences and stress to the patient. This review discusses the potential use of exhaled breath analysis as a simple, noninvasive tool for early detection of lung cancer and characterization of suspicious lung nodules.

A European Respiratory Society technical standard: exhaled biomarkers in lung disease

Breath tests cover the fraction of nitric oxide in expired gas (F_eNO), volatile organic compounds (VOCs), variables in exhaled breath condensate (EBC) and other measurements. For EBC and for F_eNO, official recommendations for standardised procedures are more than 10 years old and there is none for exhaled VOCs and particles. The aim of this document is to provide technical standards and recommendations for sample collection and analytic approaches and to highlight future research priorities in the field. For EBC and F_eNO, new developments and advances in technology have been evaluated in the current document. This report is not intended to provide clinical guidance on disease diagnosis and management.Clinicians and researchers with expertise in exhaled biomarkers were invited to participate. Published studies regarding methodology of breath tests were selected, discussed and evaluated in a consensus-based manner by the Task Force members.Recommendations for standardisation of sampling, analysing and reporting of data and suggestions for research to cover gaps in the evidence have been created and summarised.Application of breath biomarker measurement in a standardised manner will provide comparable results, thereby facilitating the potential use of these biomarkers in clinical practice.

Effects of Sampling Conditions and Environmental Factors on Fecal Volatile Organic Compound Analysis by an Electronic Nose Device

Prior to implementation of volatile organic compound (VOC) analysis in clinical practice, substantial challenges, including methodological, biological and analytical difficulties are faced. The aim of this study was to evaluate the influence of several sampling conditions and environmental factors on fecal VOC profiles, analyzed by an electronic nose (eNose). Effects of fecal sample mass, water content, duration of storage at room temperature, fecal sample temperature, number of freeze-thaw cycles and effect of sampling method (rectal swabs vs. fecal samples) on VOC profiles were assessed by analysis of totally 725 fecal samples by means of an eNose (Cyranose320®). Furthermore, fecal VOC profiles of totally 1285 fecal samples from 71 infants born at three different hospitals were compared to assess the influence of center of origin on VOC outcome. We observed that all analyzed variables significantly influenced fecal VOC composition. It was feasible to capture a VOC profile using rectal swabs, although this differed significantly from fecal VOC profiles of similar subjects. In addition, 1285 fecal VOC-profiles could significantly be discriminated based on center of birth. In conclusion, standardization of methodology is necessary before fecal VOC analysis can live up to its potential as diagnostic tool in clinical practice.

Detection of cancer through exhaled breath: a systematic review

Background

Timely diagnosis of cancer represents a challenging task; in particular, there is a need for reliable non-invasive screening tools that could achieve high levels of adherence at virtually no risk in population-based screening. In this review, we summarize the current evidence of exhaled breath analysis for cancer detection using standard analysis techniques and electronic nose.

Methods

Relevant studies were identified searching Pubmed and Web of Science databases until April 30, 2015. Information on breath test performance, such as sensitivity and specificity, was extracted together with volatile compounds that were used to discriminate cancer patients from controls. Performance of different breath analysis techniques is provided for various cancers together with information on methodological issues, such as breath sampling protocol and validation of the results.

Results

Overall, 73 studies were included, where two-thirds of the studies were conducted on lung cancer. Good discrimination usually required a combination of multiple biomarkers, and area under the receiver operating characteristic curve or accuracy reached levels of 0.9 or higher in multiple studies. In 25% of the reported studies, classification models were built and validated on the same datasets. Huge variability was seen in different aspects among the studies.

Conclusions

Analyses of exhaled breath yielded promising results, although standardization of breath collection, sample storage and data handling remain critical issues. In order to foster breath analysis implementation into practice, larger studies should be implemented in true screening settings, paying particular attention to standardization in breath collection, consideration of covariates, and validation in independent population samples.

Comparison of volatile organic compounds from lung cancer patients and healthy controls-challenges and limitations of an observational study

This paper outlines the design and performance of an observational study on the profiles of volatile organic compounds (VOCs) in the breath of 37 lung cancer patients and 23 healthy controls of similar age. The need to quantify each VOC considered as a potential disease marker on the basis of individual calibration is elaborated, and the quality control measures required to maintain reproducibility in breath sampling and subsequent instrumental trace VOC analysis using solid phase microextraction-gas chromatography-mass spectrometry over a study period of 14 months are described. Twenty-four VOCs were quantified on the basis of their previously suggested potential as cancer markers. The concentration of aromatic compounds in the breath was increased, as expected, in smokers, while lung cancer patients displayed significantly increased levels of oxygenated VOCs such as aldehydes, 2-butanone and 1-butanol. Although sets of selected oxygenated VOCs displayed sensitivities and specificities between 80% and 90% using linear discriminant analysis (LDA) with leave-one-out cross validation, the effective selectivity of the breath VOC approach with regard to cancer detection is clearly limited. Results are discussed against the background of the literature on volatile cancer marker investigations and the prospects of linking increased VOC levels in patients' breath with approaches that employ sniffer dogs. Experience from this study and the literature suggests that the currently available methodology is not able to use breath VOCs to reliably discriminate between cancer patients and healthy controls. Observational studies often tend to note significant differences in levels of certain oxygenated VOCs, but without the resolution required for practical application. Any step towards the exploitation of differences in VOC profiles for illness detection would have to solve current restrictions set by the low and variable VOC concentrations. Further challenges are the technical complexity of studies involving breath sampling and possibly the limited capability of current analytical procedures to detect unstable marker candidates.