Selected ion flow tube mass spectrometry of exhaled breath condensate headspace

A metal-organic framework loaded paper-based chemiluminescence sensor for trace acetone detection in exhaled breath

Trace acetone determination in breath can be regarded as a noninvasive method for diagnosis of diabetes. Here, a paper-based CL gas sensor combined with UiO-66 as the preconcentrator was established for sensitive detection of trace acetone in exhaled breath. UiO-66 with excellent adsorption performance and unique water stability was used for the adsorption and enrichment of acetone gas under high humidity conditions in exhaled breath. As acetone can remarkably increase the chemiluminescence (CL) of the 2,4-dinitrophenylhydrazine (DNPH)-potassium permanganate (KMnO₄) system, a sensitive CL device based on a paper substrate for trace acetone detection was established and the detection limit was 0.03 ppm. The fabricated method was used to assess the content of trace acetone in exhaled breath with satisfactory recoveries of 90-110%. It is expected to realize the noninvasive determination of acetone for diabetic patients in exhaled breath.

Biochemical Methanol Gas Sensor (MeOH Bio-Sniffer) for Non-Invasive Assessment of Intestinal Flora from Breath Methanol

Methanol (MeOH) in exhaled breath has potential for non-invasive assessment of intestinal flora. In this study, we have developed a biochemical gas sensor (bio-sniffer) for MeOH in the gas phase using fluorometry and a cascade reaction with two enzymes, alcohol oxidase (AOD) and formaldehyde dehydrogenase (FALDH). In the cascade reaction, oxidation of MeOH was initially catalyzed by AOD to produce formaldehyde, and then this formaldehyde was successively oxidized via FALDH catalysis together with reduction of oxidized form of β-nicotinamide adenine dinucleotide (NAD+). As a result of the cascade reaction, reduced form of NAD (NADH) was produced, and MeOH vapor was measured by detecting autofluorescence of NADH. In the development of the MeOH bio-sniffer, three conditions were optimized: selecting a suitable FALDH for better discrimination of MeOH from ethanol in the cascade reaction; buffer pH that maximizes the cascade reaction; and materials and methods to prevent leaking of NAD+ solution from an AOD-FALDH membrane. The dynamic range of the constructed MeOH bio-sniffer was 0.32-20 ppm, which encompassed the MeOH concentration in exhaled breath of healthy people. The measurement of exhaled breath of a healthy subject showed a similar sensorgram to the standard MeOH vapor. These results suggest that the MeOH bio-sniffer exploiting the cascade reaction will become a powerful tool for the non-invasive intestinal flora testing.

Feasibility study on exhaled-breath analysis by untargeted Selected-Ion Flow-Tube Mass Spectrometry in children with cystic fibrosis, asthma, and healthy controls: Comparison of data pretreatment and classification techniques

Selected-Ion Flow-Tube Mass Spectrometry (SIFT-MS) has been applied in a clinical context as diagnostic tool for breath samples using target biomarkers. Exhaled breath sampling is non-invasive and therefore much more patient friendly compared to bronchoscopy, which is the golden standard for evaluating airway inflammation. In the actual pilot study, 55 exhaled breath samples of children with asthma, cystic-fibrosis and healthy individuals were included. Rather than focusing on the analysis of target biomarkers or on the identification of biomarkers, different data analysis strategies, including a variety of pretreatment, classification and discrimination techniques, are evaluated regarding their capacity to distinguish the three classes based on subtle differences in their full scan SIFT-MS spectra. Proper data-analysis strategies are required because these full scan spectra contain much external, i.e. unwanted, variation. Each SIFT-MS analysis generates three spectra resulting from ion-molecule reactions of analyte molecules with H₃O⁺, NO⁺ and O₂⁺. Models were built with Linear Discriminant Analysis, Quadratic Discriminant Analysis, Soft Independent Modelling by Class Analogy, Partial Least Squares - Discriminant Analysis, K-Nearest Neighbours, and Classification and Regression Trees. Perfect models, concerning overall sensitivity and specificity (100% for both) were found using Direct Orthogonal Signal Correction (DOSC) pretreatment. Given the uncertainty related to the classification models associated with DOSC pretreatments (i.e. good classification found also for random classes), other models are built applying other preprocessing approaches. A Partial Least Squares - Discriminant Analysis model with a combined pre-processing method considering single value imputation results in 100% sensitivity and specificity for calibration, but was less good predictive. Pareto scaling prior to Quadratic Discriminant Analysis resulted in 41/55 correctly classified samples for calibration and 34/55 for cross-validation. In future, the uncertainty with DOSC and the applicability of the promising preprocessing methods and models must be further studied applying a larger representative data set with a more extensive number of samples for each class. Nevertheless, this pilot study showed already some potential for the untargeted SIFT-MS application as a rapid pattern-recognition technique, useful in the diagnosis of clinical breath samples.

Evaluation of lipid peroxidation by the analysis of volatile aldehydes in the headspace of synthetic membranes using Selected Ion Flow Tube Mass Spectrometry, SIFT-MS

RATIONALE

Oxidative stress of cell membranes leads to a number of pathological processes associated with some diseases and is accompanied by the release of volatile aldehydes, which, potentially, can be used as biomarkers. Thus, the aim was to investigate peroxidation of defined synthetic membranes by direct quantitative analysis of volatile aldehydes.

METHODS

The concentration spectra of volatile compounds present in the headspace of synthetic membranes under peroxidation stress and following mechanical stress due to sonication were obtained using solid phase microextraction (SPME) in combination with Gas Chromatography Mass Spectrometry (SPME/GC/MS) and Selected Ion Flow Tube Mass Spectrometry (SIFT-MS). The focus was on the direct, real time quantification of volatile aldehydes. In addition, the total aldehydes in the aqueous membrane suspensions were quantified using the TBARS method.

RESULTS

Propanal, butanal, pentanal, hexanal, heptanal and malondialdehyde were detected and quantified in the humid headspace of the media containing the synthetic membranes following peroxidation. The composition and concentration of these saturated aldehydes strongly depend on the unsaturated fatty acids representation in the liposomes. Some protective effect of cholesterol was observed especially for membranes peroxidised by Fenton reagents and after application of a mechanical stress.

CONCLUSIONS

This study demonstrates that peroxidation of model synthetic membranes in vitro can be tracked in real time using direct quantification by SIFT-MS of several specific aldehydes in the headspace of the membrane suspensions. Cholesterol plays an important role in retaining membrane structure and can indirectly protect membranes from lipid peroxidation.

Evaluation of peroxidative stress of cancer cells in vitro by real-time quantification of volatile aldehydes in culture headspace

RATIONALE

Peroxidation of lipids in cellular membranes results in the release of volatile organic compounds (VOCs), including saturated aldehydes. The real-time quantification of trace VOCs produced by cancer cells during peroxidative stress presents a new challenge to non-invasive clinical diagnostics, which as described here, we have met with some success.

METHODS

A combination of selected ion flow tube mass spectrometry (SIFT-MS), a technique that allows rapid, reliable quantification of VOCs in humid air and liquid headspace, and electrochemistry to generate reactive oxygen species (ROS) in vitro has been used. Thus, VOCs present in the headspace of CALU-1 cancer cell line cultures exposed to ROS have been monitored and quantified in real time using SIFT-MS.

RESULTS

The CALU-1 lung cancer cells were cultured in 3D collagen to mimic in vivo tissue. Real-time SIFT-MS analyses focused on the volatile aldehydes: propanal, butanal, pentanal, hexanal, heptanal and malondialdehyde (propanedial), that are expected to be products of cellular membrane peroxidation. All six aldehydes were identified in the culture headspace, each reaching peak concentrations during the time of exposure to ROS and eventually reducing as the reactants were depleted in the culture. Pentanal and hexanal were the most abundant, reaching concentrations of a few hundred parts-per-billion by volume, ppbv, in the culture headspace.

CONCLUSIONS

The results of these experiments demonstrate that peroxidation of cancer cells in vitro can be monitored and evaluated by direct real-time analysis of the volatile aldehydes produced. The combination of adopted methodology potentially has value for the study of other types of VOCs that may be produced by cellular damage.

Increase of methanol in exhaled breath quantified by SIFT-MS following aspartame ingestion

Aspartame, methyl-L-α-aspartyl-L-phenylalaninate, is used worldwide as a sweetener in foods and drinks and is considered to be safe at an acceptable daily intake (ADI) of 40 mg per kg of body weight. This compound is completely hydrolyzed in the gastrointestinal tract to aspartic acid, phenylalanine and methanol, each being toxic at high levels. The objective of the present study was to quantify the volatile methanol component in the exhaled breath of ten healthy volunteers following the ingestion of a single ADI dose of aspartame. Direct on-line measurements of methanol concentration were made in the mouth and nose breath exhalations using selected ion flow tube mass spectrometry, SIFT-MS, several times before aspartame ingestion in order to establish individual pre-dose (baseline) levels and then during two hours post-ingestion to track their initial increase and subsequent decrease. The results show that breath methanol concentrations increased in all volunteers by 1082   ±   205 parts-per-billion by volume (ppbv) from their pre-ingestion values, which ranged from 193 to 436 ppbv to peak values ranging from 981-1622 ppbv, from which they slowly decreased. These observations agree quantitatively with a predicted increase of 1030 ppbv estimated using a one-compartment model of uniform dilution of the methanol generated from a known amount of aspartame throughout the total body water (including blood). In summary, an ADI dose of aspartame leads to a 3-6 fold increase of blood methanol concentration above the individual baseline values.

Pitfalls in the analysis of volatile breath biomarkers: suggested solutions and SIFT-MS quantification of single metabolites

The experimental challenges presented by the analysis of trace volatile organic compounds (VOCs) in exhaled breath with the objective of identifying reliable biomarkers are brought into focus. It is stressed that positive identification and accurate quantification of the VOCs are imperative if they are to be considered as discreet biomarkers. Breath sampling procedures are discussed and it is suggested that for accurate quantification on-line real time sampling and analysis is desirable. Whilst recognizing such real time analysis is not always possible and sample collection is often required, objective recognition of the pitfalls involved in this is essential. It is also emphasized that mouth-exhaled breath is always contaminated to some degree by orally generated compounds and so, when possible, analysis of nose-exhaled breath should be performed. Some difficulties in breath analysis are mitigated by the choice of analytical instrumentation used, but no single instrument can provide solutions to all the analytical challenges. Analysis and interpretation of breath analysis data, however acquired, needs to be treated circumspectly. In particular, the excessive use of statistics to treat imperfect mass spectrometry/mobility spectra should be avoided, since it can result in unjustifiable conclusions. It is should be understood that recognition of combinations of VOCs in breath that, for example, apparently describe particular cancer states, will not be taken seriously until they are replicated in other laboratories and clinics. Finally, the inhibiting notion that single biomarkers of infection and disease will not be identified and utilized clinically should be dispelled by the exemplary and widely used single biomarkers NO and H2 and now, as indicated by recent selected ion flow tube mass spectroscopy (SIFT-MS) results, triatomic hydrogen cyanide and perhaps pentane and acetic acid. Hopefully, these discoveries will provide encouragement to research workers to be more open-minded on this important and desirable issue.

Quantitative analysis of exhaled carbonyl compounds distinguishes benign from malignant pulmonary disease

OBJECTIVES

The analysis of exhaled breath is a promising noninvasive tool for the diagnosis of lung cancer, but its clinical relevance has yet to be established. We report the analysis of exhaled volatile carbonyl compounds for the identification of specific carbonyl cancer markers to differentiate benign pulmonary disease from early-stage lung cancer and to compare its diagnostic accuracy with positron emission tomography (PET) scans.

METHODS

Aminooxy-coated silicon microchips were used for the selective capture of exhaled carbonyls by an oximation reaction. Breath samples were collected then directed through the silicon chips by applying a vacuum. Carbonyl adducts were analyzed by Fourier transform mass spectrometry. Eighty-eight control subjects, 107 patients with lung cancer (64 stage 0, I, or II), 40 patients with benign pulmonary disease, and 7 patients with a solitary pulmonary metastasis participated. Analysis of cancer markers was performed blinded to the pathologic results.

RESULTS

Four carbonyls were defined as cancer markers with significantly higher concentrations in patients with lung cancer. The number of increased cancer markers distinguished benign disease from both early and stage III and IV lung cancer. For early-stage disease, defining greater than 2 increased markers as diagnostic of lung cancer resulted in 83% sensitivity and 74% specificity. PET scans for this same cohort resulted in 90% sensitivity but only 39% specificity. Markers normalized for 3 of the 4 markers after resection of the lung cancer.

CONCLUSIONS

Analysis of specific exhaled carbonyls can differentiate early lung cancer from benign pulmonary disease. Breath analysis was more specific than PET for a lung cancer diagnosis. Judicious use of these data may expedite the care of patients with lung cancer.

Breath analysis of ammonia, volatile organic compounds and deuterated water vapor in chronic kidney disease and during dialysis

The volatile metabolites present in trace amounts in exhaled breath of healthy individuals and patients, for example those with advanced chronic kidney disease (CKD), can now be detected and quantified by sensitive analytical techniques. In this review, special attention is given to the major retention metabolites resulting from dialysis-dependent CKD stage 5 and especially ammonia, as a potential estimator of the severity of uremia. However, other biomarkers are important, including the hydrocarbons isoprene, ethane and pentane, in that they are likely to indicate tissue injury associated with the dialysis treatment itself. Evaluation of over-hydration, a serious complication of CKD stage5 can be improved by analysis of deuterium in exhaled water vapor after ingestion of a known amount of deuterated water, so providing total body water measurements at the bedside to support clinical management of volume status.

Noninvasive detection of lung cancer using exhaled breath

Early detection of lung cancer is a key factor for increasing the survival rates of lung cancer patients. The analysis of exhaled breath is promising as a noninvasive diagnostic tool for diagnosis of lung cancer. We demonstrate the quantitative analysis of carbonyl volatile organic compounds (VOCs) and identification of lung cancer VOC markers in exhaled breath using unique silicon microreactor technology. The microreactor consists of thousands of micropillars coated with an ammonium aminooxy salt for capture of carbonyl VOCs in exhaled breath by means of oximation reactions. Captured aminooxy-VOC adducts are analyzed by nanoelectrospray Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry (MS). The concentrations of 2-butanone, 2-hydroxyacetaldehyde, 3-hydroxy-2-butanone, and 4-hydroxyhexenal (4-HHE) in the exhaled breath of lung cancer patients (n = 97) were significantly higher than in the exhaled breath of healthy smoker and nonsmoker controls (n = 88) and patients with benign pulmonary nodules (n = 32). The concentration of 2-butanone in exhaled breath of patients (n = 51) with stages II though IV non-small cell lung cancer (NSCLC) was significantly higher than in exhaled breath of patients with stage I (n = 34). The carbonyl VOC profile in exhaled breath determined using this new silicon microreactor technology provides for the noninvasive detection of lung cancer.

Detection of volatile organic compounds as biomarkers in breath analysis by different analytical techniques

Breath is a rich mixture containing numerous volatile organic compounds at trace amounts (ppbv–pptv level) such as: hydrocarbons, alcohols, ketones, aldehydes, esters or heterocycles. The presence of some of them depends on health status. Therefore, breath analysis might be useful for clinical diagnostics, therapy monitoring and control of metabolic or biochemical cell cycle products. This Review presents an update on the latest developments in breath analysis applied to diagnosing different diseases with the help of high-quality equipment. Efforts were made to fully and accurately describe traditional and modern techniques used to determine the components of breath. The techniques were compared in terms of design, function and also detection limit of different volatile organic compounds. GC with different detectors, MS, optical sensor and laser spectroscopic detection techniques are also discussed.

A quantitative study of the influence of inhaled compounds on their concentrations in exhaled breath

Throughout the development of breath analysis research, there has been interest in how the concentrations of trace compounds in exhaled breath are related to their concentrations in the ambient inhaled air. In considering this, Phillips introduced the concept of 'alveolar gradient' and judged that the measured exhaled concentrations of volatile organic compounds should be diminished by an amount equal to their concentrations in the inhaled ambient air. The objective of the work described in this paper was to investigate this relationship quantitatively. Thus, experiments have been carried out in which inhaled air was polluted by seven compounds of interest in breath research, as given below, and exhaled breath has been analysed by SIFT-MS as the concentrations of these compounds in the inhaled air were reduced. The interesting result obtained is that all the exogenous compounds are partially retained in the exhaled breath and there are close linear relationships between the exhaled and inhaled air concentrations for all seven compounds. Thus, retention coefficients, a, have been derived for the following compounds: pentane, 0.76 ± 0.09; isoprene, 0.66 ± 0.04; acetone, 0.17 ± 0.03; ammonia, 0.70 ± 0.13, methanol, 0.29 ± 0.02; formaldehyde, 0.06 ± 0.03; deuterated water (HDO), 0.09 ± 0.02. From these data, correction to breath analyses for inhaled concentration can be described by coefficients specific to each compound, which can be close to 1 for hydrocarbons, as applied by Phillips, or around 0.1, meaning that inhaled concentrations of such compounds can essentially be neglected. A further deduction from the experimental data is that under conditions of the inhalation of clean air, the measured exhaled breath concentrations of those compounds should be increased by a factor of 1/(1 - a) to correspond to gaseous equilibrium with the compounds dissolved in the mixed venous blood entering the alveoli. Thus, for isoprene, this is a factor of 3, which we have confirmed experimentally by re-breathing experiments.

Recent trend in risk assessment of formaldehyde exposures from indoor air

Studies about formaldehyde (FA) published since the guideline of 0.1 mg/m(3) by the World Health Organization (WHO) in 2010 have been evaluated; critical effects were eye and nasal (portal-of-entry) irritation. Also, it was considered to prevent long-term effects, including all types of cancer. The majority of the recent toxicokinetic studies showed no exposure-dependent FA-DNA adducts outside the portal-of-entry area and FA-DNA adducts at distant sites were due to endogenously generated FA. The no-observed-adverse-effect level for sensory irritation was 0.5 ppm and recently reconfirmed in hypo- and hypersensitive individuals. Investigation of the relationship between FA exposure and asthma or other airway effects in children showed no convincing association. In rats, repeated exposures showed no point mutation in the p53 and K-Ras genes at ≤15 ppm neither increased cell proliferation, histopathological changes and changes in gene expression at 0.7 ppm. Repeated controlled exposures (0.5 ppm with peaks at 1 ppm) did not increase micronucleus formation in human buccal cells or nasal tissue (0.7 ppm) or in vivo genotoxicity in peripheral blood lymphocytes (0.7 ppm), but higher occupational exposures were associated with genotoxicity in buccal cells and cultivated peripheral blood lymphocytes. It is still valid that exposures not inducing nasal squamous cell carcinoma in rats will not induce nasopharyngeal cancer or lymphohematopoietic malignancies in humans. Reproductive and developmental toxicity are not considered relevant in the absence of sensory irritation. In conclusion, the WHO guideline has been strengthened.

A novel microreactor approach for analysis of ketones and aldehydes in breath

We report a fabricated microreactor with thousands of micropillars in channels. Each micropillar surface is chemically functionalized to selectively preconcentrate gaseous ketones and aldehydes of exhaled breath and to enhance ultra-trace, rapid analysis by direct-infusion Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry (MS). The micropillar reactive coating contains the quaternary ammonium aminooxy salt 2-(aminooxy)ethyl-N,N,N-trimethylammonium iodide (ATM) for capturing trace carbonyl VOCs by means of an oximation reaction. We demonstrate the utility of this approach for detection of C(1) to C(12) aldehydes and ketones in exhaled breath, but the approach is applicable to any gaseous sample.

Ambient analysis of trace compounds in gaseous media by SIFT-MS

The topic of ambient gas analysis has been rapidly developed in the last few years with the evolution of the exciting new techniques such as DESI, DART and EESI. The essential feature of all is that analysis of trace gases can be accomplished either in the gas phase or those released from surfaces, crucially avoiding sample collection or modification. In this regard, selected ion flow tube mass spectrometry, SIFT-MS, also performs ambient analyses both accurately and rapidly. In this focused review we describe the underlying ion chemistry underpinning SIFT-MS through a discourse on the reactions of different classes of organic and inorganic molecules with H(3)O(+), NO(+) and O(2)(+)˙ studied using the SIFT technique. Rate coefficients and ion products of these reactions facilitate absolute SIFT-MS analyses and can also be useful for the interpretation of data obtained by the other ambient analysis methods mentioned above. The essential physics and flow dynamics of SIFT-MS are described that, together with the reaction kinetics, allow SIFT-MS to perform absolute ambient analyses of trace compounds in humid atmospheric air, exhaled breath and the headspace of aqueous liquids. Several areas of research that, through pilot experiments, are seen to benefit from ambient gas analysis using SIFT-MS are briefly reviewed. Special attention is given to exhaled breath and urine headspace analysis directed towards clinical diagnosis and therapeutic monitoring, and some other areas researched using SIFT-MS are summarised. Finally, extensions to current areas of application and indications of other directions in which SIFT-MS can be exploited for ambient analysis are alluded to.

Progress in SIFT-MS: breath analysis and other applications

The development of selected ion flow tube mass spectrometry, SIFT-MS, is described from its inception as the modified very large SIFT instruments used to demonstrate the feasibility of SIFT-MS as an analytical technique, towards the smaller but bulky transportable instruments and finally to the current smallest Profile 3 instruments that have been located in various places, including hospitals and schools to obtain on-line breath analyses. The essential physics and engineering principles are discussed, which must be appreciated to design and construct a SIFT-MS instrument. The versatility and sensitivity of the Profile 3 instrument is illustrated by typical mass spectra obtained using the three precursor ions H(3)O(+), NO(+) and O(2)(+)·, and the need to account for differential ionic diffusion and mass discrimination in the analytical algorithms is emphasized to obtain accurate trace gas analyses. The performance of the Profile 3 instrument is illustrated by the results of several pilot studies, including (i) on-line real time quantification of several breath metabolites for cohorts of healthy adults and children, which have provided representative concentration/population distributions, and the comparative analyses of breath exhaled via the mouth and nose that identify systemic and orally-generated compounds, (ii) the enhancement of breath metabolites by drug ingestion, (iii) the identification of HCN as a marker of Pseudomonas colonization of the airways and (iv) emission of volatile compounds from urine, especially ketone bodies, and from skin. Some very recent developments are discussed, including the quantification of carbon dioxide in breath and the combination of SIFT-MS with GC and ATD, and their significance. Finally, prospects for future SIFT-MS developments are alluded to.

Clinical applications of breath testing

Breath testing has the potential to benefit the medical field as a cost-effective, non-invasive diagnostic tool for diseases of the lung and beyond. With growing evidence of clinical worth, standardization of methods, and new sensor and detection technologies the stage is set for breath testing to gain considerable attention and wider application in upcoming years.