The novel selected-ion flow tube approach to trace gas analysis of air and breath

Ammonia measurement in human breath of subjects with Helicobacter pylori using photoacoustic spectroscopy

Helicobacter pylori (H. pylori) is a type of bacteria that infects the stomach. The detection of H. pylori is an essential part of current clinical practices because this disease can cause peptic ulcers, chronic inflammation of the stomach lining but also stomach cancer. Helicobacter pylori has a naturally occurring enzyme that hydrolyzes urea into ammonium carbonate called urease. Many methods exist for the detection of H. pylori infection, but an innovative approach is to detect the ammonia in the breath (ABT, Ammonia Breath Test). In this research study, using photoacoustic spectroscopy method, the ammonia concentration in the breathing zone of people with H. pylori were measured and were compared with ammonia concentration from the respiration of healthy people. From the ABT determinations of this study, the ammonia was established to be increased with 498 ppb at people with H. pylori when we compare with ABT of healthy people.

Robust Automated SIFT-MS Quantitation of Volatile Compounds in Air Using a Multicomponent Gas Standard

Selected ion flow tube mass spectrometry, SIFT-MS, has been widely used in industry and research since its introduction in the mid-1990s. Previously described quantitation methods have been advanced to include a gas standard for a more robust and repeatable analytical performance. The details of this approach to calculate the concentrations from ion-molecule reaction kinetics based on reaction times and instrument calibration functions determined from known concentrations in the standard mix are discussed. Important practical issues such as the overlap of product ions are outlined, and best-practice approaches are presented to enable them to be addressed during method development. This review provides a fundamental basis for a plethora of studies in broad application areas that are possible with SIFT-MS instruments.

Increasing the Robustness of SIFT-MS Volatilome Fingerprinting by Introducing Notional Analyte Concentrations

Selected ion flow tube-mass spectrometry (SIFT-MS) is an analytical technique for volatile detection and quantification. SIFT-MS can be applied in a "white box" approach, measuring concentrations of target compounds, or as a "black box" fingerprinting technique, scanning all product ions during a full scan. Combining SIFT-MS full scan data acquired from multibatches or large-scale experiments remains problematic due to signal fluctuation over time. The standard approach of normalizing full scan data to the total signal intensity was insufficient. This study proposes a new approach to correct SIFT-MS fingerprinting data. In this concept, all of the product ions from a full scan are considered individual compounds for which notional concentrations can be calculated. Converting ion count rates into notional analyte concentrations accounts for any changes in the instrument parameters. The benefits of the proposed approach are demonstrated on three years of data from both multibatches and long-term experiments showing a significant reduction of system-induced fluctuations providing a better focus on the changes of interest.

A measurement and modelling investigation of the indoor air chemistry following cooking activities

Domestic cooking is a source of indoor air pollutants, including volatile organic compounds (VOCs), which can impact on indoor air quality. However, the real-time VOC emissions from cooking are not well characterised, and similarly, the resulting secondary chemistry is poorly understood. Here, selected-ion flow-tube mass spectrometry (SIFT-MS) was used to monitor the real-time VOC emissions during the cooking of a scripted chicken and vegetable stir-fry meal, in a room scale, semi-realistic environment. The VOC emissions were dominated by alcohols (70% of total emission), but also contained a range of aldehydes (14%) and terpenes (5%), largely attributable to the heating of oil and the preparation and heating of spices, respectively. The direct cooking-related VOC emissions were then simulated using the Indoor Chemical Model in Python (INCHEM-Py), to investigate the resulting secondary chemistry. Modelling revealed that VOC concentrations were dominated by direct emissions, with only a small contribution from secondary products, though the secondary species were longer lived than the directly emitted species. Following cooking, hydroxyl radical concentrations reduced by 86%, while organic peroxy radical levels increased by over 700%, later forming secondary organic nitrates, peroxyacylnitrates (PANs) and formaldehyde. Monoterpene emissions were shown to drive the formation of secondary formaldehyde, albeit to produce relatively modest concentrations (average of 60 ppt). Sensitivity analysis of the simulation conditions revealed that increasing the outdoor concentrations of ozone and NOx species (2.9× and 9×, respectively) resulted in the greatest increase in secondary product formation indoors (≈400%, 200% and 600% increase in organic nitrates, PANs and formaldehyde production, respectively). Given the fact that climate change is likely to result in increased ozone concentrations in the future, and that increased window-opening in response to rising temperatures is also likely, higher concentrations of indoor oxidants are likely in homes in the future. This work, therefore, suggests that cooking could be a more important source of secondary pollutants indoors in the future.

Direct mass spectrometry analysis of exhaled human breath in real-time

The molecular composition of exhaled human breath can reflect various physiological and pathological conditions. Considerable progress has been achieved over the past decade in real-time analysis of exhaled human breath using direct mass spectrometry methods, including selected ion flow tube mass spectrometry, proton transfer reaction mass spectrometry, extractive electrospray ionization mass spectrometry, secondary electrospray ionization mass spectrometry, acetone-assisted negative photoionization mass spectrometry, atmospheric pressure photoionization mass spectrometry, and low-pressure photoionization mass spectrometry. Here, recent developments in direct mass spectrometry analysis of exhaled human breath are reviewed with regard to analytical performance (chemical sensitivity, selectivity, quantitative capabilities) and applications of the developed methods in disease diagnosis, targeted molecular detection, and real-time metabolic monitoring.

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.

Recent Advances in Sensing Materials Targeting Clinical Volatile Organic Compound (VOC) Biomarkers: A Review

In general, volatile organic compounds (VOCs) have a high vapor pressure at room temperature (RT). It has been reported that all humans generate unique VOC profiles in their exhaled breath which can be utilized as biomarkers to diagnose disease conditions. The VOCs available in exhaled human breath are the products of metabolic activity in the body and, therefore, any changes in its control level can be utilized to diagnose specific diseases. More than 1000 VOCs have been identified in exhaled human breath along with the respiratory droplets which provide rich information on overall health conditions. This provides great potential as a biomarker for a disease that can be sampled non-invasively from exhaled breath with breath biopsy. However, it is still a great challenge to develop a quick responsive, highly selective, and sensitive VOC-sensing system. The VOC sensors are usually coated with various sensing materials to achieve target-specific detection and real-time monitoring of the VOC molecules in the exhaled breath. These VOC-sensing materials have been the subject of huge interest and extensive research has been done in developing various sensing tools based on electrochemical, chemoresistive, and optical methods. The target-sensitive material with excellent sensing performance and capturing of the VOC molecules can be achieved by optimizing the materials, methods, and its thickness. This review paper extensively provides a detailed literature survey on various non-biological VOC-sensing materials including metal oxides, polymers, composites, and other novel materials. Furthermore, this review provides the associated limitations of each material and a summary table comparing the performance of various sensing materials to give a better insight to the readers.

Ternary association reactions of H3 O+ , NO+ and O2 +• with N2 , O2 , CO2 and H2 O; implications for selected ion flow tube mass spectrometry analyses of air and breath

RATIONALE

The reactions of the reagent ions used for trace gas analysis in selected ion flow tube mass spectrometry (SIFT-MS), R⁺ , viz. H₃ O⁺ , NO⁺ and O₂ ⁺ , with the major gases in air and breath samples, M, viz. N₂ , O₂ , CO₂ and H₂ O, are investigated. These reactions are seen to form weakly-bound adduct ions, R⁺ M, by ternary association reactions that must not be mistaken for genuine volatile organic compound (VOC) analyte ions.

METHODS

The ternary association rate coefficients mediated by helium (He) carrier gas atoms, k_3a , have been determined for all combinations of R⁺ and M, which form R⁺ M adduct ions ranging in m/z from 47 (H₃ O⁺ N₂ ) to 76 (O₂ ^+• CO₂ ). This was achieved by adding variable amounts of M (up to 0.5 mbar pressure) into the He carrier gas (pressure of 1.33 mbar) in a SIFT-MS flow tube at 300 K. Parabolic curvature was observed on some of the semi-logarithmic decay curves that allowed the rate coefficients mediated by M molecules, k_3b , to be estimated.

RESULTS

Values of k_3a were found to range from 1 × 10^-31  cm⁶  s^-1 to 5 × 10^-29  cm⁶  s^-1 , which form mass spectral R⁺ M "ghost peaks" of significant strength when analysing VOCs at parts-per-billion concentrations. It was seen that the R⁺ M adduct ions (except when M is H₂ O) react with H₂ O molecules by ligand switching forming the readily recognised monohydrates of the initial reagent cations R⁺ H₂ O. Whilst this ligand switching diminishes the R⁺ M adduct ghost peaks, it does not eliminate them entirely.

CONCLUSIONS

The significance of these adduct ions for trace gas analysis by SIFT-MS in the low m/z region is alluded to, and some examples are given of m/z spectral overlaps of the R⁺ M and R⁺ H₂ O adduct cations with analyte cations of VOCs formed by analysis of complex media like exhaled breath, warning that ghost peaks will be enhanced using nitrogen carrier gas in SIFT-MS.

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 ^+• .

Sensitivity of secondary electrospray ionization mass spectrometry to a range of volatile organic compounds: Ligand switching ion chemistry and the influence of Zspray™ guiding electric fields

RATIONALE

Secondary electrospray ionization (SESI) is currently only semi-quantitative. In the Zspray™ arrangement of SESI-MS, the transfer of ions from near atmospheric pressure to a triple quadrupole is achieved by guiding electric fields that partially desolvate both reagent and analyte ions which must be understood. Also, to make SESI-MS more quantitative, the mechanisms and the kinetics of the reaction processes, especially ligand switching reactions of hydrated hydronium reagent ions, H₃ O⁺ (H₂ O)_n , with volatile organic compound (VOC) molecules, need to be understood.

METHODS

A modified Zspray™ ESI ion source operating at sub-atmospheric pressure with analyte sample gas introduced via an inlet coaxial with the spray was used. Variation of the ion-guiding electric fields was used to reveal the degree of desolvation of both reagent and analyte ions. The instrument sensitivity was determined for several classes of VOCs by introducing bag samples of suitably varying concentrations as quantified on-line using selected ion flow tube MS.

RESULTS

Electric field desolvation resulted in largely protonated VOCs, MH⁺ , and their monohydrates, MH⁺ H₂ O, and for some VOCs proton-bound dimer ions, MH⁺ M, were formed. There was a highly linear response of the ion signal to the measured VOC sample concentration, which provided the instrument sensitivities, S, for 25 VOCs. The startling results show very wide variations in S from near 0 to 1 for hydrocarbons, and up to 100, on a relative scale, for polar compounds such as monoketones and unsaturated aldehydes.

CONCLUSIONS

The complex ion chemistry occurring in the SESI ion source, largely involving gas-phase ligand switching, results in widely variable sensitivities for different classes of VOCs. The sensitivity is observed to depend on the dipole moment and proton affinity of the analyte VOC molecule, M, and to decrease with the observed fraction of MH⁺ H₂ O, but other yet unrecognized factors must play a significant role.

Early Warning Diagnostics for Emerging Infectious Diseases in Developing into Late-Stage Pandemics

The spread of infectious diseases due to travel and trade can be seen throughout history, whether from early settlers or traveling businessmen. Increased globalization has allowed infectious diseases to quickly spread to different parts of the world and cause widespread infection. Posthoc analysis of more recent outbreaks-SARS, MERS, swine flu, and COVID-19-has demonstrated that the causative viruses were circulating through populations for days or weeks before they were first detected, allowing disease to spread before quarantines, contact tracing, and travel restrictions could be implemented. Earlier detection of future novel pathogens could decrease the time before countermeasures are enacted. In this Account, we examined a variety of novel technologies from the past 10 years that may allow for earlier detection of infectious diseases. We have arranged these technologies chronologically from pre-human predictive technologies to population-level screening tools. The earliest detection methods utilize artificial intelligence to analyze factors such as climate variation and zoonotic spillover as well as specific species and geographies to identify where the infection risk is high. Artificial intelligence can also be used to monitor health records, social media, and various publicly available data to identify disease outbreaks faster than traditional epidemiology. Secondary to predictive measures is monitoring infection in specific sentinel animal species, where domestic animals or wildlife are indicators of potential disease hotspots. These hotspots inform public health officials about geographic areas where infection risk in humans is high. Further along the timeline, once the disease has begun to infect humans, wastewater epidemiology can be used for unbiased sampling of large populations. This method has already been shown to precede spikes in COVID-19 diagnoses by 1 to 2 weeks. As total infections increase in humans, bioaerosol sampling in high-traffic areas can be used for disease monitoring, such as within an airport. Finally, as disease spreads more quickly between humans, rapid diagnostic technologies such as lateral flow assays and nucleic acid amplification become very important. Minimally invasive point-of-care methods can allow for quick adoption and use within a population. These individual diagnostic methods then transfer to higher-throughput methods for more intensive population screening as an infection spreads. There are many promising early warning technologies being developed. However, no single technology listed herein will prevent every future outbreak. A combination of technologies from across our infection timeline would offer the most benefit in preventing future widespread disease outbreaks and pandemics.

Revealing dynamic changes of the volatile profile of food samples using PTR-MS

Volatile compounds carry valuable information regarding the properties of foodstuffs. Volatiles emitted from food can be used as, for example, indicators of quality, shelf-life, or authenticity. A better understanding of the multitude of transformations which occur during food processing could facilitate the optimisation of production, increase the desirability of food products, and also their wholesomeness. However, as some of these transformations are fast-paced, it is necessary to monitor them using techniques which enable real-time determination of volatiles, such as proton transfer reaction-mass spectrometry (PTR-MS). Recent years have seen a marked increase in its use in food analysis, since it can be used to obtain insight into the dynamics of the monitored processes and can be the basis for precise quality control methods for food processing. This review highlights recent works in which PTR-MS was used in monitoring during foodstuffs production, preparation and storage.

Botanical and geographical origin of Turkish honeys by selected-ion flow-tube mass spectrometry and chemometrics

BACKGROUND

Honey has a very important commercial value for producers as a natural product. Honey aroma is formed from the contributions of several volatile compounds, which are influenced by nectar composition, botanical origins, and location. Selected-ion flow-tube mass spectrometry (SIFT-MS) is a technique that quantifies volatile organic compounds simply and rapidly, even in low concentrations. In this study, the headspace concentration of eight monofloral (chestnut, rhododendron, lavender, sage, carob, heather, citrus, and pine) and three multiflower Turkish honeys were analyzed using SIFT-MS. Soft independent modeling of class analogy (SIMCA) was used to differentiate honey samples based on their volatiles.

RESULTS

This study focused on 78 volatile compounds, which were selected from previous studies of selected honeys. Very clear distinctions were observed between all honeys. Interclass distances greater than 8 indicate that honeys were significantly different. Methanol and ethanol were abundant in the honeys. Chestnut honey collected from the Yalova region had the highest total concentration of volatiles followed by heather honey and chestnut honey collected from the Düzce region.

CONCLUSION

Honeys with different botanical and geographical origins showed differences in their volatile profile based on chemometric analysis. Of the honey samples, methanol, ethanol, acetoin, ethyl acetate, and isobutanoic acid had the highest discriminating power. Methanol and ethanol, and then acetic acid, were the volatiles with the highest concentrations in most honeys. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Dynamic headspace analysis using online measurements: Modeling of average and initial concentration

Dynamic headspace sampling is an important technique for the analysis of consumer products, the study of biological samples and environmental water analyses. This paper shows the influence of experimental conditions, such as the sampling time, sampling flow rate, headspace volume, liquid volume and Henry coefficient on the measured average concentration values. A corresponding closed expression as function of these variables is introduced in order to quantify the deviation of the initial headspace concentration. The proposed bi-exponential function embeds different current existing models for recovery calculation in dynamic sampling analyses in one single expression. A fully automated and user-friendly Excel^® file to investigate or to model the dynamic headspace sampling results is added to everyone's easy use.

Non-separative mass spectrometry methods for non-invasive medical diagnostics based on volatile organic compounds: A review

In this review, an assessment of non-separative methods based on mass spectrometry used to analyse volatile organic compounds in the field of bioanalysis is performed. The use of non-separative methods based on mass spectrometry has been established as an attractive option for analysing compounds. These instrumental configurations are suitable for biomedical applications because of their versatility, rapid output of results, and the wide range of volatile organic compounds that can be determined. Here, techniques such as headspace sampling coupled to mass spectrometry, membrane introduction mass spectrometry, selected ion flow tube mass spectrometry, proton transfer reaction mass spectrometry, secondary electrospray ionization mass spectrometry and ion mobility mass spectrometry, are evaluated. Samples involving non-invasive methods of collection, such as urine, saliva, breath and sweat, are mainly considered. To the best of our knowledge, a comprehensive review of all the non-separative instrumental configurations applied to the analysis of gaseous samples from all matrices non-invasively collected has not yet been carried out. The assessment of non-separative techniques for the analysis of these type of samples can be considered a key issue for future clinical applications, as they allow real-time sample analysis, without patient suffering. Any contribution to the early diagnosis of disease can be considered a priority for the scientific community. Therefore, the identification and determination of volatile organic compounds related to particular diseases has become an important field or research.

Ion chemistry at elevated ion–molecule interaction energies in a selected ion flow-drift tube: reactions of H3O+, NO+ and O2+ with saturated aliphatic ketones

Rate coefficients and product ion branching ratios determined for proton transfer, association and charge transfer reactions provide insight into reaction mechanisms.

A Pilot Study of Ion - Molecule Reactions at Temperatures Relevant to the Atmosphere of Titan

Reliable theoretical models of the chemical kinetics of the ionosphere of Saturn's moon, Titan, is highly dependent on the precision of the rates of the reactions of ambient ions with hydrocarbon molecules at relevant temperatures. A Variable Temperature Selected Ions Flow Tube technique, which has been developed primarily to study these reactions at temperatures within the range of 200-330 K, is briefly described. The flow tube temperature regulation system and the thermalisation of ions are also discussed. Preliminary studies of two reactions have been carried out to check the reliability and efficacy of kinetics measurements: (i) Rate constants of the reaction of CH3+ ions with molecular oxygen were measured at different temperatures, which indicate values in agreement with previous ion cyclotron resonance measurements ostensibly made at 300 K. (ii) Formation of CH3+ ions in the reaction of N2+ ions with CH4 molecules were studied at temperatures within the range 240-310 K which showed a small but statistically significant decrease of the ratio of product CH3+ ions to reactant N2+ ions with reaction temperature.

Deodorization of Garlic Breath by Foods, and the Role of Polyphenol Oxidase and Phenolic Compounds

Garlic causes a strong garlic breath that may persist for almost a day. Therefore, it is important to study deodorization techniques for garlic breath. The volatiles responsible for garlic breath include diallyl disulfide, allyl mercaptan, allyl methyl disulfide, and allyl methyl sulfide. After eating garlic, water (control), raw, juiced or heated apple, raw or heated lettuce, raw or juiced mint leaves, or green tea were consumed immediately. The levels of the garlic volatiles on the breath were analyzed from 1 to 60 min by selected ion flow tube mass spectrometry (SIFT-MS). Garlic was also blended with water (control), polyphenol oxidase (PPO), rosemarinic acid, quercetin or catechin, and the volatiles in the headspace analyzed from 3 to 40 min by SIFT-MS. Raw apple, raw lettuce, and mint leaves significantly decreased all of the garlic breath volatiles in vivo. The proposed mechanism is enzymatic deodorization where volatiles react with phenolic compounds. Apple juice and mint juice also had a deodorizing effect on most of the garlic volatiles but were generally not as effective as the raw food, probably because the juice had enzymatic activity but the phenolic compounds had already polymerized. Both heated apple and heated lettuce produced a significant reduction of diallyl disulfide and allyl mercaptan. The presence of phenolic compounds that react with the volatile compounds even in the absence of enzymes is the most likely mechanism. Green tea had no deodorizing effect on the garlic volatile compounds. Rosmarinic acid, catechin, quercetin, and PPO significantly decreased all garlic breath volatiles in vitro. Rosmarinic acid was the most effective at deodorization.

Technologies for Clinical Diagnosis Using Expired Human Breath Analysis

This review elucidates the technologies in the field of exhaled breath analysis. Exhaled breath gas analysis offers an inexpensive, noninvasive and rapid method for detecting a large number of compounds under various conditions for health and disease states. There are various techniques to analyze some exhaled breath gases, including spectrometry, gas chromatography and spectroscopy. This review places emphasis on some of the critical biomarkers present in exhaled human breath, and its related effects. Additionally, various medical monitoring techniques used for breath analysis have been discussed. It also includes the current scenario of breath analysis with nanotechnology-oriented techniques.

SIFT-MS and FA-MS methods for ambient gas phase analysis: developments and applications in the UK

The origins of SIFT created to study interstellar chemistry and SIFT-MS developed for ambient gas and exhaled breath analysis and the UK centres in which these techniques are being exploited.

Breath analysis in disease diagnosis: methodological considerations and applications

Breath analysis is a promising field with great potential for non-invasive diagnosis of a number of disease states. Analysis of the concentrations of volatile organic compounds (VOCs) in breath with an acceptable accuracy are assessed by means of using analytical techniques with high sensitivity, accuracy, precision, low response time, and low detection limit, which are desirable characteristics for the detection of VOCs in human breath. "Breath fingerprinting", indicative of a specific clinical status, relies on the use of multivariate statistics methods with powerful in-built algorithms. The need for standardisation of sample collection and analysis is the main issue concerning breath analysis, blocking the introduction of breath tests into clinical practice. This review describes recent scientific developments in basic research and clinical applications, namely issues concerning sampling and biochemistry, highlighting the diagnostic potential of breath analysis for disease diagnosis. Several considerations that need to be taken into account in breath analysis are documented here, including the growing need for metabolomics to deal with breath profiles.

Laser-based method and sample handling protocol for measuring breath acetone

A robust method is demonstrated to measure acetone in human breath at sub parts-per-million by volume (ppmv) concentrations using diode laser cavity enhanced absorption spectroscopy. The laser operates in the near-infrared at about 1690 nm probing overtone transitions in acetone in a spectral region relatively free from interference from common breath species such as CO2, water, and methane. Using an optical cavity with a length of 45 cm, bound by mirrors of 99.997% reflectivity, a limit of detection of ∼180 parts-per-billion by volume (ppbv) (1σ) of breath acetone is achieved. The method is validated with measurements made with an ion-molecule reaction mass spectrometer. A technique to calibrate the optical cavity mirror reflectivity using a temperature dependent water vapor source is also described.

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.

Monitoring of human chemical signatures using membrane inlet mass spectrometry

This work is an attempt to assist border security crackdown on illegal human immigration, by providing essential results on human chemical signatures. Data was obtained using a portable quadrupole mass spectrometer coupled with a membrane probe for volunteers of both genders and under different conditions in a container simulator. During experiments, participants were asked to follow various protocols while volatile organic compounds emitted from their breath, sweat, skin, and other biological excretes were continuously being monitored. Experimental setups using different membrane materials (both hydrophilic and hydrophobic) including heating of the sampling probe and sampling flow rates were examined. From our measurements, significant information was obtained for NH3, CO2, water, and volatile organic compounds levels, illustrating a human chemical profile and indicating human presence in a confined space.

On the features, successes and challenges of selected ion flow tube mass spectrometry

The major features of the selected ion flow tube mass spectrometry (SIFT-MS) analytical method that was conceived and designed for the analysis, in real time, of air obviating sample collections into bags or extraction by pre-concentration of trace compounds onto surfaces are reviewed. The unique analytical capabilities of SIFT-MS for ambient analysis are stressed that allow quantification of volatile organic and inorganic compounds directly from the measurement of physical parameters without the need for regular instrumental calibration using internal or external standards. Then, emphasis is placed on the challenging real-time accurate analysis of single exhalations of humid breath, which is now achieved and readily facilitates wider applications of SIFT-MS in other fields where trace gas analysis has value. The quality of the data obtained by SIFT-MS is illustrated by the quantification of some exhaled breath metabolites that are of immediate relevance to physiology and medicine, including that of hydrogen cyanide in the breath of patients with cystic fibrosis. The current status of SIFT-MS is revealed by a form of a strengths, weakness, opportunities and threats (SWOT) analysis intended to present an objective view of this analytical technique and the likely way forward towards its further development and application.

Selected ion flow tube-MS analysis of headspace vapor from gastric content for the diagnosis of gastro-esophageal cancer

Gastric content is a complex biofluid within the human stomach which has an important role in digestive processes. It is believed that gastric content may be a contributory factor in the development of upper gastro-intestinal diseases. In this work, selected ion flow tube mass spectrometry (SIFT-MS) has been applied to the quantification of volatile organic compounds (VOCs) in the headspace vapor of gastric content samples, which were retrieved from three groups of patients, including those with gastro-esophageal cancer, noncancer diseases of the upper gastro-intestinal tract, and a healthy cohort. Twelve VOCs have been investigated in this study; the following 7 VOCs, acetone, formaldehyde, acetaldehyde, hexanoic acid, hydrogen sulphide, hydrogen cyanide, and methyl phenol, were found to be significantly different between cancer and healthy groups by the Mann-Whitney U test. Receiver operating characteristics (ROC) analysis was applied for the combined VOCs of acetaldehyde, formaldehyde, hydrogen sulphide, and methyl phenol to discriminate cancer patients from healthy controls. The area under the curve (AUC) was 0.9. This result raises the prospect that a VOC profile rather than a single biomarker may be preferable in the molecular-orientated diagnosis of gastro-oseophageal cancer, and this warrants further investigation to assess its potential application as a new diagnostic test.

Microbial volatile compounds in health and disease conditions

Microbial cultures and/or microbial associated diseases often have a characteristic smell. Volatile organic compounds (VOCs) are produced by all microorganisms as part of their normal metabolism. The types and classes of VOC produced is wide, including fatty acids and their derivatives (e.g. hydrocarbons, aliphatic alcohols and ketones), aromatic compounds, nitrogen containing compounds, and volatile sulfur compounds. A diversity of ecological niches exist in the human body which can support a polymicrobial community, with the exact VOC profile of a given anatomical site being dependent on that produced by both the host component and the microbial species present. The detection of VOCs is of interest to various disciplines, hence numerous analytical approaches have been developed to accurately characterize and measure VOCs in the laboratory, often from patient derived samples. Using these technological advancements it is evident that VOCs are indicative of both health and disease states. Many of these techniques are still largely confined to the research laboratory, but it is envisaged that in future bedside 'VOC profiling' will enable rapid characterization of microbial associated disease, providing vital information to healthcare practitioners.

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.

Advances in electronic-nose technologies developed for biomedical applications

The research and development of new electronic-nose applications in the biomedical field has accelerated at a phenomenal rate over the past 25 years. Many innovative e-nose technologies have provided solutions and applications to a wide variety of complex biomedical and healthcare problems. The purposes of this review are to present a comprehensive analysis of past and recent biomedical research findings and developments of electronic-nose sensor technologies, and to identify current and future potential e-nose applications that will continue to advance the effectiveness and efficiency of biomedical treatments and healthcare services for many years. An abundance of electronic-nose applications has been developed for a variety of healthcare sectors including diagnostics, immunology, pathology, patient recovery, pharmacology, physical therapy, physiology, preventative medicine, remote healthcare, and wound and graft healing. Specific biomedical e-nose applications range from uses in biochemical testing, blood-compatibility evaluations, disease diagnoses, and drug delivery to monitoring of metabolic levels, organ dysfunctions, and patient conditions through telemedicine. This paper summarizes the major electronic-nose technologies developed for healthcare and biomedical applications since the late 1980s when electronic aroma detection technologies were first recognized to be potentially useful in providing effective solutions to problems in the healthcare industry.

Comparison of volatile release in tomatillo and different varieties of tomato during chewing

The release of volatiles from tomatillos (Physalis ixocarpa Brot.) and tomatoes in the mouthspace and nosespace was measured in real-time using selected ion flow tube mass spectrometry (SIFT-MS). (Z)-3-Hexenal, (E)-2-hexenal, hexanal, and 1-penten-3-one increased, while isobutyl alcohol, nonanal, and methylbutanal showed no significant change in the first 30 s of chewing. Cherry tomato released more (E)-2-hexenal, (Z)-3-hexenal, and 1-penten-3-one than tomatillo, Roma tomato, and vine-ripened tomato during chewing. The proportion of the average concentration of volatiles in the mouthspace after swallowing to before swallowing (MSas/MSbs) varied from 2.8% to 73.9% between different volatiles and varieties. Methylbutanal, hexanal, and nonanal were retained at a higher percentage in the mouth after swallowing than (Z)-3-hexenal, (E)-2-hexenal, 1-penten-3-one, and isobutyl alcohol. The proportion of the average volatile concentration in the mouthspace, to the headspace in a glass container (MS/HS) of 1-penten-3-one, hexanal, methylbutanal, and nonanal, and the proportion of nosespace to headspace (NS/HS) for 1-penten-3-one, hexanal, (Z)-3-hexenal, and nonanal was significantly higher in tomatillo than in tomatoes. There was no difference between tomatoes of different varieties in NS/HS ratio.

PRACTICAL APPLICATION

The real-time volatile release from tomatillos and tomatoes was measured and compared. The information obtained on the dynamic generation of volatile compounds provides a better understanding of volatile release in the headspace of tomatillo and tomatoes. The compounds and their volatile release patterns were similar for the tomatillo and tomatoes. The green aldehydes released during chewing were not significantly higher than most tomato varieties, except for Roma tomatoes. Cherry tomato released relatively more volatiles during chewing, whereas Roma tomatoes were generally poor in mouthspace volatiles. The lingering of volatiles in the mouth after swallowing was different for different volatiles and varieties, which may appear as a sensory difference detected by consumers.

Differences in exhaled gas profiles between patients with type 2 diabetes and healthy controls

AIMS

Recent advances in analytical technology allow the detection of several hundred volatile organic compounds (VOCs) in human exhaled air, many of which reflect unidentified endogenous pathways. This study was performed to determine whether a breath gas analysis using proton transfer reaction-mass spectrometry (PTR-MS) could serve as a noninvasive method to distinguish between patients with type 2 diabetes mellitus and healthy controls.

METHODS

Breath and room air samples were measured from 21 patients with insulin-treated type 2 diabetes and 26 healthy controls. VOCs in the mass range of 20-200 atomic mass units were analyzed using PTR-MS.

RESULTS

We identified eight masses characteristic of endogenous VOCs that showed significant differences in the gas profiles of patients with type 2 diabetes and healthy control subjects. Using these VOCs for linear discriminant analysis, the sensitivity and specificity were found to be 90% and 92%, respectively.

CONCLUSIONS

These results suggest that it is possible to separate patients with diabetes mellitus type 2 from healthy controls by multivariate analysis of exhaled endogenous VOCs. This is a first step towards the development of a noninvasive test using breath gas of at-risk persons and making it an attractive option for large-scale testing of at-risk populations. However, the establishment of exhaled volatiles as metabolic markers requires additional confirmatory investigations.

Evaluation of selected-ion flow-tube mass spectrometry for the measurement of ethanol, methanol and isopropanol in physiological fluids: effect of osmolality and sample volume

Selected-ion flow-tube mass spectrometry (SIFT-MS) is particularly suited for the analysis of volatile low molecular weight compounds. We have evaluated this technique for the assay of different alcohols in aqueous solutions, including blood plasma, and in particular whether the osmolality or sample volume affected vapourisation. Solutions of three different alcohols (methanol, ethanol and isopropanol) ranging from 0.005 to 50 mmol/L were prepared in deionised water (0 milliosmol), phosphate-buffered saline (690 mOsm), isotonic saline (294 mOsm) and plasma (296 mOsm). The vapour above the sample (50 to 1000 microL) contained in air-tight tubes at 37 degrees C was aspirated into the instrument. The outputs for ethanol, methanol and isopropanol were linear over the concentration range and independent of the sample volume and relatively independent of the osmolar concentration. SIFT-MS can reliably and accurately measure common alcohols in the headspace above aqueous solutions, including serum/plasma. This novel application of SIFT-MS is easy to follow, requires no sample preparation and the wide dynamic range will facilitate measurement of alcohols present from normal metabolism as well as when taken in excess or in accidental poisoning.

Expression of the gas-transporting proteins, Rh B glycoprotein and Rh C glycoprotein, in the murine lung

A family of gas-transporting proteins, the Mep/Amt/Rh glycoprotein family, has been identified recently. These are integral membrane proteins, are widely expressed in sites of gas transport, and are known to transport the gaseous molecule, NH(3), and recent evidence indicates they can transport CO(2). Because the mammalian lung is a critical site for gas transport, the current studies examine the expression of the nonerythroid members of this extended family, Rh B glycoprotein (Rhbg) and Rh C glycoprotein (Rhcg), in the normal mouse lung. Real-time RT-PCR and immunoblot analysis demonstrated both Rhbg and Rhcg mRNA and protein expression, respectively. Immunohistochemistry demonstrated both Rhbg and Rhcg were expressed in bronchial and bronchiolar epithelial cells. Rhbg was expressed by Clara cells, specifically, whereas all bronchial/bronchiolar epithelial cells, with the exception of goblet cells, expressed Rhcg. Rhbg expression was basolateral, whereas Rhcg exhibited apical and intracellular immunolabel, polarized expression similar to that observed in Rhbg- and Rhcg-expressing epithelial cells in other organs. There was no detectable expression of either Rhbg or Rhcg in alveolar endothelial or epithelial cells, in pneumocytes or in vascular tissue. In vitro studies using cultured bronchial epithelial cells confirm Rhbg and Rhcg expression, demonstrate that saturable, not diffusive, transport is the primary mechanism of ammonia/methylammonia transport, and show that the saturable transport mechanism has kinetics similar to those demonstrated previously for Rhbg and Rhcg. These findings suggest Rhbg and Rhcg may contribute to bronchial epithelial cell ammonia metabolism and suggest that they do not contribute to pulmonary CO(2) transport.