Proton Transfer Reaction Time-of-flight Mass Spectrometry Research Articles

Rapid and direct identification of the origin of white tea with proton transfer reaction time-of-flight mass spectrometry.

White tea has become very popular in recent years, but there has been no scientific identification of white tea from different origins. For product authentication and valorization, every kind of white tea must be marked with an indication of its origin. Volatile profiles of white tea leaf samples from their main origins in China (Fuding City, Zhenghe City and Jianyang City) were analyzed using proton transfer reaction time-of-flight mass spectrometry (PTR-TOFMS). Tentative identifications of the volatile organic compounds (VOCs) were obtained by PTR-TOFMS of the headspace. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were performed to evaluate the differences among the various origins. Teas from different origins were shown to have characteristic VOCs and profiles. Thus, white teas from different origins could be separated by characterizing the volatile emissions from the dry tea leaves. The ability of the two classification models to use the volatile fingerprints in origin discrimination was investigated. Two classification models (PCA and OPLS-DA) were applied to the PTR-TOFMS data obtained from the VOCs of various white teas. The classification models were shown to be useful in identifying the origin of white tea samples, providing a reference for white tea identification.

Development of a Novel Phenotypic Roadmap to Improve Blueberry Quality and Storability.

Improved fruit quality and prolonged storage capability are key breeding traits for blueberry (Vaccinium spp.) fruit. Until now, breeding selection was mostly oriented on the amelioration of agronomic traits, such as flowering time, chilling requirement, or plant structure. Up until now, however, the storage effect on fruit quality has not been extensively studied, mostly because objective and handy phenotyping tools to evaluate quality traits were not available. In this study we are proposing a novel phenotyping protocol to support breeding selection and quality control within the entire blueberry production chain. Volatile organic compounds (VOCs) and texture traits, were measured by Proton Transfer Reaction- Time of Flight- Mass Spectrometry (PTR-ToF-MS) and a texture analyzer respectively, taking into consideration the influence of prolonged storage. The exploitation of the genetic variability existing within the investigated blueberry germplasm collection (including both southern and northern highbush, hybrids, and rabbiteyes) allowed the identification of the best performing cultivars, based on texture and VOCs variability, to be used as superior parental lines for future breeding programs. The comprehensive characterization of blueberry aroma allowed the identification of a wide array of spectrometric features, mostly related to aldehydes, alcohols, terpenoids, and esters, that can be used as putative biomarkers to rapidly evaluate the blueberry aroma variations related to genetic differences and storability. In addition, this study revealed a lack of straightforward relationship between harvest and postharvest quality features, that might be genotype-dependent.

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

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

Monoterpene Chemical Speciation with High Time Resolution Using a FastGC/PTR-MS: Results from the COV3ER Experiment on Quercus ilex

Monoterpenes (MTs) represent an important family of biogenic volatile organic compounds (BVOCs) in terms of amount and chemical diversity. This family has been extensively studied using gas chromatography (GC) and proton transfer reaction-mass spectrometry (PTR-MS). Upon recent advances with Fast Gas Chromatography (FastGC), it was also commercialized with proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) instruments. The combination of both techniques showed promising results in the near real-time separation of isomers, with the need of further improvements. In this study, a FastGC prototype was coupled to a conventional PTR-MS (PTR-QuadMS). Extensive laboratory experiments were performed, in order to test the system’s performance and to optimize its operational parameters for MT separation. The detection limit was determined to be around 0.8–1.7 ppbv, depending on the MT. The system was afterwards deployed during a three-week field campaign in a mixed holm oak (Quercus ilex) forest known for its important MT emissions. MTs were measured in the incoming and the outgoing air of dynamic enclosures installed on the branches of four different trees. Three chemotypes of holm oak trees could be distinguished showing consistently different proportions of the emitted MTs throughout the measurement campaign: pinene-type, myrcene-type and limonene-type. Measurements showed a systematic diel variation in emissions typical of light and temperature-dependent, de novo-synthesized VOCs. The results demonstrated the feasibility of the FastGC/PTR-MS system for continuous measurements from dynamic chambers in the field, whereas further improvements would be necessary to lower the detection limit for ambient air measurements.

Photochemical transformation of residential wood combustion emissions: dependence of organic aerosol composition on OH exposure

Abstract. Residential wood combustion (RWC) emits large amounts of gaseous and particulate organic aerosol (OA). In the atmosphere, the emission is transformed via oxidative reactions, which are under daylight conditions driven mainly by hydroxyl radicals (OH). This continuing oxidative ageing produces secondary OA and may change the health- and climate-related properties of the emission. However, it is not well known how the composition of RWC-originated OA changes as the function of OH exposure. In this work, emissions from two modern residential logwood combustion appliances were photochemically aged in an oxidation flow reactor (OFR) with various OH exposure levels, reaching up to 6×1011 s cm−3 (equivalent to 1 week in the atmosphere). Gaseous organic compounds were analysed by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), while particulate OA was analysed online by a high-resolution soot particle aerosol mass spectrometer (SP-HR-ToF-AMS) and offline by in situ derivatization thermal desorption–gas chromatography–time-of-flight mass spectrometry (IDTD-GC-ToF-MS). Photochemical reactions increased the mass of particulate organic carbon by a factor of 1.3–3.9. The increase in mass took place during the first atmospheric equivalent day of ageing, after which the enhancement was independent of the extent of photochemical exposure. However, ageing increased the oxidation state of the particulate OA linearly throughout the assessed range, with ΔH:C/ΔO:C slopes between −0.17 and −0.49 in van Krevelen space. Ageing led to an increase in acidic fragmentation products in both phases, as measured by the IDTD-GC-ToF-MS for the particulate and PTR-ToF-MS for the gaseous phase. For the gaseous organic compounds, the formation of small carbonylic compounds combined with the rapid degradation of primary volatile organic compounds such as aromatic compounds led to a continuous increase in both the O : C and H : C ratios. Overall, the share of polycyclic aromatic compounds (PACs) in particles degraded rapidly during ageing, although some oxygen-substituted PACs, most notably naphthaldehydic acid, increased, in particular during relatively short exposures. Similarly, the concentrations of particulate nitrophenols rose extensively during the first atmospheric equivalent day. During continuous photochemical ageing, the dominant transformation mechanisms shifted from the initial gas-phase functionalization/condensation to the transformation of the particulate OA by further oxidation reactions and fragmentation. The observed continuous transformation of OA composition throughout a broad range of OH exposures indicates that the entire atmospheric lifetime of the emission needs to be explored to fully assess the potential climate and health effects of RWC emissions.

Vertical profiles of biogenic volatile organic compounds as observed online at a tower in Beijing

Vertical profiles of isoprene and monoterpenes were measured by a proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) at heights of 3, 15, 32, 64, and 102 m above the ground on the Institute of Atmospheric Physics (IAP) tower in central Beijing during the winter of 2016 and the summer of 2017. Isoprene mixing ratios were larger in summer due to much stronger local emissions whereas monoterpenes were lower in summer due largely to their consumption by much higher levels of ozone. Isoprene mixing ratios were the highest at the 32 m in summer (1.64 ± 0.66 ppbV) and at 15 m in winter (1.41 ± 0.64 ppbV) with decreasing concentrations to the ground and to the 102 m, indicating emission from the tree canopy of the surrounding parks. Monoterpene mixing ratios were the highest at the 3 m height in both the winter (0.71 ± 0.42 ppbV) and summer (0.16 ± 0.10 ppbV) with a gradual decreasing trend to 102 m, indicting an emission from near the ground level. The lowest isoprene and monoterpene mixing ratios all occurred at 102 m, which were 0.71 ± 0.42 ppbV (winter) and 1.35 ± 0.51 ppbV (summer) for isoprene, and 0.42 ± 0.22 ppbV (winter) and 0.07 ± 0.06 ppbV (summer) for monoterpenes. Isoprene in the summer and monoterpenes in the winter, as observed at the five heights, showed significant mutual correlations. In the winter monoterpenes were positively correlated with combustion tracers CO and acetonitrile at 3 m, suggesting possible anthropogenic sources.

Novel experimental approach to study aroma release upon reconstitution of instant coffee products

This study presents an experimental approach to study the kinetics and fast release of volatile organic compounds (VOCs) upon reconstitution of instant coffee products. A sampling setup coupled to PTR-ToF-MS (Proton Transfer Reaction Time-of-Flight Mass Spectrometry) for the automated and reproducible reconstitution of instant coffee products was developed to monitor the dynamic release of VOCs. A rapid release of aroma compounds was observed in the first seconds upon hot water addition (“aroma burst”), followed by subsequent decrease in headspace (HS) intensities over the course of analysis. Differences in time-intensity release profiles of individual VOCs were correlated to their Henry’s Law constant, vapor pressure and water solubility. The setup and approach proposed here have shown to be sensitive and to respond to fast dynamic changes in aroma release. It allows studying VOCs release upon reconstitution and supports the development of novel technologies and formulations for instant products with improved aroma release properties.

Studies pertaining to the monitoring of volatile halogenated anaesthetics in breath by proton transfer reaction mass spectrometry

Post-operative isoflurane has been observed to be present in the end-tidal breath of patients who have undergone major surgery, for several weeks after the surgical procedures. A major new non-controlled, non-randomized, and open-label approved study will recruit patients undergoing various surgeries under different inhalation anaesthetics, with two key objectives, namely (1) to record the washout characteristics following surgery, and (2) to investigate the influence of a patient’s health and the duration and type of surgery on elimination. In preparation for this breath study using proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS), it is important to identify first the analytical product ions that need to be monitored and under what operating conditions. In this first paper of this new research programme, we present extensive PTR-TOF-MS studies of three major anaesthetics used worldwide, desflurane (CF3CHFOCHF2), sevoflurane ((CF3)2CHOCH2F), and isoflurane (CF3CHClOCHF2) and a fourth one, which is used less extensively, enflurane (CHF2OCF2CHFCl), but is of interest because it is an isomer of isoflurane. Product ions are identified as a function of reduced electric field (E/N) over the range of approximately 80 Td to 210 Td, and the effects of operating the drift tube under ‘normal’ or ‘humid’ conditions on the intensities of the product ions are presented. To aid in the analyses, density functional theory (DFT) calculations of the proton affinities and the gas-phase basicities of the anaesthetics have been determined. Calculated energies for the ion-molecule reaction pathways leading to key product ions, identified as ideal for monitoring the inhalation anaesthetics in breath with a high sensitivity and selectivity, are also presented.

Spatial and temporal distribution characteristics and ozone formation potentials of volatile organic compounds from three typical functional areas in China

BackgroundOzone is currently one of the most important air pollutants. Volatile organic compounds (VOCs) can easily react with atmospheric radicals to form ozone. In-field measurement of VOCs may help in estimating the local VOC photochemical pollution level. MethodThis study examined the spatial and temporal distribution characteristics of VOCs during winter at three typical sites of varying classification in China; industrial (Guangzhou Economic and Technological Development District (GETDD)), urban (Guangzhou higher education mega center (HEMC)), and rural (Pingyuan county (PYC)), using Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS). ResultsThe concentrations of total VOCs (TVOCs) at the GETDD, HEMC and PYC sites were 352.5, 129.2 and 75.1 ppb, respectively. The dominant category of VOCs is nitrogen-containing VOCs (NVOCs, accounting for 43.3% of TVOCs) at GETDD, of which C4H11N (m/z+ = 74.10, butyl amine) was the predominant chemical species (80.5%). In contrast, oxygenated VOCs (OVOCs) were the most abundant at HEMC and PYC, accounting for 60.2% and 64.1% of the total VOCs, respectively; here, CH4O (m/z+ = 33.026, methanol) was the major compound, accounting for 40.5% of the VOCs at HEMC and 50.9% at PYC. The ratios of toluene to benzene (T/B) were calculated for different measured sites, as the ratios of T/B can reveal source resolution of aromatic VOCs. The average contributions to total ozone formation potentials (OFP) of the total measured VOCs in each area were 604.9, 315.9 and 111.7 μg/m3 at GETDD, HEMC and PYC, respectively; the highest OFP contributors of the identified VOCs were aliphatic hydrocarbons (AlHs) at GETDD, aromatic hydrocarbons (AHs) at HEMC, and OVOCs at PYC. ConclusionsOFP assessment indicated that the photochemical pollution caused by VOCs at GETDD was serious, and was also significant in the HEMC region. The dominant VOC OFP groups (AlHs and AHs) should be prioritized for control, in order to help reduce these effects.

Removal of volatile organic compounds (VOCs) emitted from a textile dyeing wastewater treatment plant and the attenuation of respiratory health risks using a pilot-scale biofilter

The textile dyeing is a significant worldwide economic pillar of the industry mainstay of the region’s industrial economy. Therefore, significant attention should be paid to its emitted volatile organic compounds (VOCs) regarding their potential adverse effects on ecosystems and human health. In this study, a spray tower (ST) (preferential elimination of hydrosoluble VOCs) and biofilter (primary removal of particle-free VOCs) were used in combination. Three techniques, including gas chromatography-mass spectrometer (GC-MS), e-nose, and Proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) were used to accurately identify the associated VOCs profile. In total, 50 types of VOCs, with total concentrations ranging from 1.26 to 2.79 mg m−3, were detected from the outlet of the TDWTP over a 90-day treatment period. The highest level occurred for nitrogen- and oxygen-containing compounds (NAOCCs), followed by aliphatic hydrocarbons (AIHs), aromatic hydrocarbons (AHs), and halogenated hydrocarbons (HHs). Average removal efficiencies (REs) of the four studied VOC groups (NAOCCs, AIHs, AHs, and HHs) were 66.7%, 67.9%, 11.7%, and 52.1%, respectively. Proteobacteria dominated the biofilter, followed by Actinobacteria, Firmicutes, and Bacteroidetes. A positive correlation was observed between the relative abundance of Proteobacteria and the RE of NAOCCs, with RE significantly increased from 38.1% (day 1) to 83.2% (day 90). The degradation of these organic pollutants, such as NAOCCs, may be mainly performed by the dominant genus, such as Acidithiobacillus and Metallibacterium, as predicted by PICRUSt. A respiratory health risk evaluation demonstrated that the cancer and non-cancer risks of typical VOCs were dramatically reduced after the above-mentioned purification. The combined results indicate that the ST-biofilter is an efficient approach for the end-of-pipe treatment of exhausted gas in TDWTP and helps attenuate human health risk.

Discrimination and geo-spatial mapping of atmospheric VOC sources using full scan direct mass spectral data collected from a moving vehicle.

Volatile and semi-volatile organic compounds (S/VOCs) are ubiquitous in the environment, come from a wide variety of anthropogenic and biogenic sources, and are important determinants of environmental and human health due to their impacts on air quality. They can be continuously measured by direct mass spectrometry techniques without chromatographic separation by membrane introduction mass spectrometry (MIMS) and proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). We report the operation of these instruments in a moving vehicle, producing full scan mass spectral data to fingerprint ambient S/VOC mixtures with high temporal and spatial resolution. We describe two field campaigns in which chemometric techniques are applied to the full scan MIMS and PTR-ToF-MS data collected with a mobile mass spectrometry lab. Principal Component Analysis (PCA) has been successfully employed in a supervised analysis to discriminate VOC samples collected near known VOC sources including internal combustion engines, sawmill operations, composting facilities, and pulp mills. A Gaussian mixture model and a density-based spatial clustering of application with noise (DBSCAN) algorithm have been used to identify sample clusters within the full time series dataset collected and we present geospatial maps to visualize the distribution of VOC sources measured by PTR-ToF-MS.

On-line profiling of volatile compounds produced in vitro by pathogenic oral bacteria

Infections by oral pathogens are one of the most common health problems worldwide. Due to the intimate connection between exhaled breath and the oral cavity, breath analysis could potentially be used to diagnose these infections. However, little is known about the volatile emissions of important oral pathogens that are connected with gingivitis and periodontitis. In this study, we have performed in vitro headspace measurements on four important oral pathogens (P. gingivalis, T. forsythia, P. intermedia and P. nigrescens) using proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS). Some of the most abundant compounds produced by the bacteria include hydrogen sulphide, methanethiol, acetone, dimethylsulphide, isoprene, cyclopentanone and indole as tentatively assigned from the mass spectra. Several other abundant mass signals were recorded but the assignment of these is less certain. Some of the bacterial species can be separated from each other by the emitted volatile fingerprints. The results of this study can be used in potential development of a diagnostic breath test for oral infections. In addition, as several of the measured compounds are known to be toxic, the results point to an intriguing possibility of studying the connection between the bacterial virulence and the emitted volatile compounds.

OH chemistry of non-methane organic gases (NMOGs) emitted from laboratory and ambient biomass burning smoke: evaluating the influence of furans and oxygenated aromatics on ozone and secondary NMOG formation

Abstract. Chamber oxidation experiments conducted at the Fire Sciences Laboratory in 2016 are evaluated to identify important chemical processes contributing to the hydroxy radical (OH) chemistry of biomass burning non-methane organic gases (NMOGs). Based on the decay of primary carbon measured by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), it is confirmed that furans and oxygenated aromatics are among the NMOGs emitted from western United States fuel types with the highest reactivities towards OH. The oxidation processes and formation of secondary NMOG masses measured by PTR-ToF-MS and iodide-clustering time-of-flight chemical ionization mass spectrometry (I-CIMS) is interpreted using a box model employing a modified version of the Master Chemical Mechanism (v. 3.3.1) that includes the OH oxidation of furan, 2-methylfuran, 2,5-dimethylfuran, furfural, 5-methylfurfural, and guaiacol. The model supports the assignment of major PTR-ToF-MS and I-CIMS signals to a series of anhydrides and hydroxy furanones formed primarily through furan chemistry. This mechanism is applied to a Lagrangian box model used previously to model a real biomass burning plume. The customized mechanism reproduces the decay of furans and oxygenated aromatics and the formation of secondary NMOGs, such as maleic anhydride. Based on model simulations conducted with and without furans, it is estimated that furans contributed up to 10 % of ozone and over 90 % of maleic anhydride formed within the first 4 h of oxidation. It is shown that maleic anhydride is present in a biomass burning plume transported over several days, which demonstrates the utility of anhydrides as markers for aged biomass burning plumes.

Airborne measurements of particulate organic matter by proton-transfer-reaction mass spectrometry (PTR-MS): a pilot study

Abstract. Herein we report on the first successful airborne deployment of the CHemical Analysis of AeRosol ONline (CHARON) particle inlet which allowed us to measure the chemical composition of atmospheric submicrometer particles in real time using a state-of-the-art proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) analyzer. The data were collected aboard the NASA DC-8 Airborne Science Laboratory on 26 June 2018 over California in the frame of NASA's Student Airborne Research Program (SARP). We show exemplary data collected when the airplane (i) shortly encountered a fresh (<1 h old) smoke plume that had emanated from the Lions Fire in the Sierra Nevada, (ii) intercepted a particle plume emitted from an amine gas treating unit of a petroleum refinery close to Bakersfield, (iii) carried out a spatial survey in the boundary layer over the San Joaquin Valley and (iv) performed a vertical profile measurement over the greater Bakersfield area. The most important finding from this pilot study is that the CHARON PTR-ToF-MS system measures fast enough to be deployed on a jet research aircraft. The data collected during 3 to 15 s long plume encounters demonstrate the feasibility of airborne point or small area emission measurements. Further improvements are, however, warranted to eliminate or reduce the observed signal tailing (1/e decay time between 6 and 20 s). The fast time response of the analyzer allowed us to generate highly spatially resolved maps (1–2 km in the horizontal, 100 m in the vertical) of atmospheric particle chemical constituents. The chemical information that was extracted from the recorded particle mass spectra includes (i) mass concentrations of ammonium, nitrate and total organics; (ii) mass concentrations of different classes of organic compounds (CH vs. CHO vs. CHN vs. CHNO compounds; monoaromatic vs. polyaromatic compounds); (iii) aerosol bulk average O:C‾ and H:C‾ ratios; (iv) mass concentrations of selected marker molecules (e.g., levoglucosan in particles emitted from a wildfire, an alkanolamine in particles emitted from a petroleum refinery) and (v) wildfire emission ratios (Δtotal organics/ΔCO = 0.054; Δlevoglucosan/ΔCO = 7.9×10-3; Δvanillic acid/ΔCO = 4.4×10-4 and Δretene/ΔCO = 1.9×10-4; all calculated as peak area ratios, in grams per gram). The capability of the CHARON PTR-ToF-MS instrument to chemically characterize submicrometer atmospheric particles in a quantitative manner, at the near-molecular level, and in real time brings a new and unprecedented measurement capability to the airborne atmospheric science community.

Nectarine volatilome response to fresh-cutting and storage

The offer of fresh-cut peaches and nectarines represents a valid alternative for stone fruit commercialization and matches the increasing market demand of ready-to-eat (RTE) products.In this study we explored the effect of fruit processing and storage on the volatilome of RTE fresh-cut nectarine. Fruit of three cultivars were sliced and packed in an industrial line and stored for 5 d at 5 °C. Volatile organic compound (VOC) evolution was assessed daily in both intact and processed fruit by an exhaustive untargeted analysis, performed by proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) and solid phase microextraction- gas chromatography-mass spectrometry (SPME/GC-MS).Fresh-cut processing induced a major variation in nectarine volatilome depending on genetic differences and storage. This volatilome amelioration may be considered as an applicable strategy to enhance peach and nectarine perceived quality. Moreover, results of this study allowed the detection of a set of possible biomarkers enabling the selection of the best nectarine genotypes for processing and the prediction of the product shelf life based on the release of flavours and off-flavours.

Simultaneous Proton Transfer Reaction-Mass Spectrometry and electronic nose study of the volatile compounds released by Plasmodium falciparum infected red blood cells in vitro

The discovery that Volatile Organic Compounds (VOCs) can be biomarkers for several diseases has led to the conception of their possible application as diagnostic tools. In this study, we aimed at defining of diagnostic signatures for the presence of malaria transmissible stages in infected individuals. To do this, we compared VOCs released by asexual and sexual stage cultures of Plasmodium falciparum, the deadliest species of malaria, with those emitted by uninfected red blood cells (RBCs). VOC analysis was carried out with an innovative set-up, where each sample was simultaneously analysed by proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS) and an electronic nose. PTR-Tof-MS results show that sexual stages are characterized by a larger emission of hexanal, compared with uninfected or asexual stage-infected RBCs, which makes them clearly identifiable. PTR-Tof-MS analysis also detected differences in VOC composition between asexual stages and uninfected RBCs. These results have been substantially replicated by the electronic nose analysis and may open the possibility to develop sensitive and easy-to-use devices able to detect sexual parasite stages in infected individuals. This study also demonstrates that the combination of mass spectrometry with electronic noses is a useful tool to identify markers of diseases and to support the development of optimized sensors.

Proton transfer reaction time-of-flight mass spectrometric measurements of volatile compounds contained in peppermint oil capsules of relevance to real-time pharmacokinetic breath studies

With the growing interest in the use of breath volatiles in the health sciences, the lack of standardization for the sampling and analysis of exhaled breath is becoming a major issue leading to an absence of conformity, reproducibility and reliability in spectrometric measurements. Through the creation of a worldwide ‘peppermint consortium’, the International Association of Breath Research has set up a task force to deal with this problem. Pharmacokinetic studies are proposed, and a real-time analytical technique that is being used is proton transfer reaction-time-of-flight-mass spectrometry (PTR-ToF-MS). This paper presents details on how the volatile compounds contained in a peppermint oil capsule, and hence on breath, appear in a PTR-ToF-MS. To aid that study, the key volatiles in the headspace of peppermint oil were first identified using gas chromatography-mass spectrometry, notably: menthol, menthone, 1,8-cineole, menthofuran, limonene, α-pinene and β-pinene. A PTR-ToF-MS analysis of these compounds has been undertaken, divorced from the complexity of the peppermint oil matrix using ‘normal’ and ‘saturated’ humidity drift-tube conditions, with the latter used to mimic breath samples, and over a range of reduced electric fields. There are no characteristic product ions that can distinguish monoterpenes and 1,8-cineole, and hence, without pre-separation, a combined washout for these volatiles can only be provided. By operating the drift tube above about 130 Td, there are characteristic product ions for menthone, menthofuran and menthol, namely m/z 155.14 (protonated menthone), m/z 151.11 (protonated menthofuran), m/z 139.15 (loss of H2O from protonated menthol) and m/z 83.09 (a fragment ion, C6H11+, from menthol). These have been used to monitor, with a high specificity, the temporal profile of these three compounds in breath following the ingestion of a peppermint oil capsule. To aid in the analyses, the proton affinities and gas-phase basicities for the key volatiles investigated have been determined using density functional theory.

Correlation between VOC fingerprinting and antimicrobial activity of several essential oils extracted by plant resins against A. tumefaciens and P. savastanoi

AbstractThe present work aimed to assess the antimicrobial activity of twelve essential oils extracted from plant resins of trees that grow in several tropical and subtropical regions of the world. Eleven essential oils were extracted from resins of plant belonging to the Burseraceae family (the genera Boswellia, Commiphora, Canarium and Bursera); the remaining oil was extracted from a resinous plant belonging to the Fabaceae family (genus Hymenea). The extraction was carried out using a conventional distillation method. The volatile organic compounds (VOCs) of each essential oil were analyzed with PTR‐ToF‐MS (proton transfer reaction time‐of‐flight mass spectrometry) and the antimicrobial activity was evaluated against the phytopathogens Agrobacterium tumefaciens and Pseudomonas savastanoi pv. savastanoi. The essential oils obtained from Boswellia papyrifera, B. dalzielii, B. frereana and B. rivae were the most abundant in terms of signal intensity and VOC number in comparison with the other analyzed essential oils. Furthermore, B. neglecta shared a common volatile profile with the Canarium species, as was demonstrated previously in the literature. Greater bacterial growth inhibition of A. tumefaciens was detected with the essential oils extracted from plants belonging to Boswellia species while less action was observed against P. savastanoi. Finally, a positive correlation was found between terpenes and terpenoid compounds and bacterial growth inhibition, suggesting these essential oils as a new source of bioactive compounds for the prevention, protection and treatment of plant diseases.

Crowd monitoring in dairy cattle—real-time VOC profiling by direct mass spectrometry

Volatile organic compounds (VOCs) emitted from breath, faeces or skin may reflect physiological and pathological processes in vivo. Our setup employs real-time proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) to explore VOC emissions of dairy cows in stable air under field conditions. Within one herd of 596 cows, seven groups (8–117 cows per group) were assessed. Groups differed in milk yield and health status (two contained cows with paratuberculosis, a chronic intestinal infection). Each group arrived one after another in the area of air measurement in front of the milking parlour. A customised PTR-TOF-MS system with a 6 m long and heated transfer line, was used for measuring VOCs continuously for 7 h, 1.5 m above the cows. Three consecutive time periods were investigated. Twenty-seven VOCs increased while the animals were gathering in the waiting area, and decreased when the animals entered the milking parlour. Linear correlations between the number of animals present and VOC concentrations were found for (C4H6)H+ and (C3H6O)H+. A relatively high concentration of acetone above the cows that had recently given birth to a calf might be related to increased fat turnover due to calving and different nutrition. Changes in VOC emissions were related to the presence of animals with paratuberculosis, to different average milk yields per group and to the time of the day (morning versus noon milking time). We found that VOC monitoring of stable air may provide additional immediate information on an animal’s metabolic or health status and foster novel applications in the field of breath research.

Effects of elevated oxygen levels on VOC analysis by means of PTR-ToF-MS

Proton-transfer-reaction-time-of-flight-mass-spectrometry (PTR-ToF-MS) is a powerful tool for real-time monitoring of volatile organic compound (VOC) profiles in human breath. However, varying oxygen concentrations in the sample matrix may influence results from VOC analysis by PTR-ToF-MS. Elevated oxygen concentrations are likely to occur in clinical settings, but also when respiratory masks or breathing apparatus are used (e.g. in scuba diving, aviation, firefighting). Oxygen concentration may vary between subjects or within the course of a measurement or study and thus bias results. We systematically assessed the effect of high O2 concentrations (up to 90%) in the sample matrix on the results of PTR-MS analysis for a pattern of VOCs including aromatics, aldehydes and ketones in dry and humid samples. In vivo experiments in healthy volunteers and mechanically ventilated animals were done to test the effect under real-life conditions. H3O+ count significantly decreased by more than 40% when the amount of oxygen in the sample matrix was increased. Almost all investigated VOCs were significantly effected by varying oxygen concentrations and differences in signal intensities of more than 50% could be observed. The effect was generally more pronounced in dry samples but still significant under humid conditions. A linear dependency of sensitivity on the oxygen concentration in the sample matrix was observed for a number of VOCs (e.g. aldehydes) possibly enabling a factor based correction. VOC intensities were also influenced under in vivo conditions, e.g. ethanol decreased up to 71%. When PTR-MS analysis is carried out under oxygen supply, these issues need to be carefully considered.