[Lindinger2005] "Unambiguous identification of volatile organic compounds by proton-transfer reaction mass spectrometry coupled with GC/MS.",
, vol. 77, no. 13: NestlÃ© Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland., pp. 4117–4124, Jul, 2005.
Interest in on-line measurements of volatile organic compounds (VOCs) is increasing, as sensitive, compact, and affordable direct inlet mass spectrometers are becoming available. Proton-transfer reaction mass spectrometry (PTR-MS) distinguishes itself by its high sensitivity (low ppt range), high time resolution (200 ms), little ionization-induced fragmentation, and ionization efficiency independent of the compound to be analyzed. Yet, PTR-MS has a shortcoming. It is a one-dimensional technique that characterizes compounds only via their mass, which is not sufficient for positive identification. Here, we introduce a technical and analytical extension of PTR-MS, which removes this shortcoming, while preserving its salient and unique features. Combining separation of VOCs by gas chromatography (GC) with simultaneous and parallel detection of the GC effluent by PTR-MS and electron impact MS, an unambiguous interpretation of complex PTR-MS spectra becomes feasible. This novel development is discussed on the basis of characteristic performance parameters, such as resolution, linear range, and detection limit. The recently developed drift tube with a reduced reaction volume is crucial to exploit the full potential of the setup. We illustrate the performance of the novel setup by analyzing a complex food system.
[Simpraga2012] "Understanding the link between photosynthesis, growth and emissions of biogenic volatile organic compounds (BVOCs) in beech, oak and ash",
: Ghent University, 2012.
Gas exchange between vegetation and the atmosphere is very dynamic. In addition to gases such as carbon dioxide (CO2), water vapor, oxygen, nitrogen oxides (NOx), sulphur dioxide, ammonia and ozone (O3), also biogenic volatile organic compounds (BVOCs) are exchanged between the vegetation and the atmosphere. This PhD focussed on the exchange of CO2 and BVOCs, since net photosynthesis (Pn) and BVOC emission are two plant processes important in plant functioning. Vegetation, and forests in particular, acts as a major source of BVOCs. The importance of the study lays in understanding the link between Pn, BVOC emissions and tree growth. BVOC emissions indirectly affect climate change as BVOCs are in combination with atmospheric NOx the main precursors of photochemical O3 in the troposphere, where it acts as potential greenhouse gas, damaging vegetation and affecting human respiratory organs. BVOCs are therefore dominant reactive compounds in the troposphere and important in atmospheric chemistry and climatology. Understanding tree chemistry and ecophysiology is crucial to predict future changes in the Earth’s carbon balance as well as to update BVOC inventories and improve predictions in tropospheric air chemistry. Accordingly, the main goals of the PhD were to identify and quantify the effects of temperature, drought, seasonality and vertical canopy gradients on Pn and BVOC emissions. The general methodology consisted of developing and constructing enclosure systems for gas exchange measurements indoors and outdoors, where coupling of an infra-red gas analysis (IRGA), proton transfer reaction-mass spectrometry (PTR-MS) and thermal desorption gas chromatography/mass spectrometry (TD-GC/MS) represented a major challenge. With respect to tree species, the focus was on European beech (Fagus sylvatica L.), while additionally common ash (Fraxinus excelsior L.) and northern red oak (Quercus rubra L.) were examined in Chapter 4. The trees were examined in growth room conditions, at the campus and in the Aelmoeseneie experimental forest. The main variables measured were Pn and BVOC emissions, in particular of monoterpenoids (MTs). In addition, microclimatic variables (air temperature, photosynthetic photon flux density, soil water potential, and vapor pressure deficit) and leaf characteristics (specific leaf area, leaf temperature, leaf pigments, and leaf water potentials) were measured. In the growth room experiments, stem diameter variations and chlorophyll indices were measured to explain the behavior of MT emissions by young beech trees. In the forest, the experimental tower showed to be an important facility for adequate local characterization of adult beech Pn and BVOC chemistry. Leaf level studies showed to be crucial for unraveling the mechanisms behind the emission of BVOCs. The results indicated a large variability in BVOC emission patterns of different tree species. Temperature, drought, seasonality, vertical canopy gradients differently influenced Pn and BVOC emissions (and in particular MTs), as well as their ratio. Indoors and outdoors day-time Pn, MT emissions and MT/Pn carbon ratio varied in a systematic manner following light and temperature changes. The results indicated that not only light affected Pn, MT emissions and MT/Pn ratio, but also showed a pronounced temperature effect on MT emissions (and hence on the MT/Pn carbon ratio), with an increasing exponential trend with rising air temperatures. Furthermore, during drought stress MT emissions showed an increasing-decreasing trend depending on the drought severity. Linear variable displacement transducers (LVDTs) showed to be useful for stress quantification in BVOC studies. Another notable finding was that, under severe drought stress, two PTR-MS signals diverged from each other, indicating the possible presence of BVOC species other than MT such as green leaf volatiles (GLVs). Seasonal measurements on anatomically different trees indicated a strong temperature rather than light dependency when looking at total BVOC emission trends. Beside substantial quantities of MTs released from leaves into the atmosphere, driven by light and temperature, beside non-MTs, MTs also showed to play a role in plant-insect interactions. Detected stress compounds proved infestiation-based emissions. Consequently, plant-insect relationships require additional research, identifying individual MT species using the GC/MS speciation approach and looking at their relationships with ecophysiological parameters. In conclusion, the performed indoor and outdoor studies demonstrated that Pn and BVOC emissions are strongly interrelated. Proposed hypotheses were tested and confirmed. However, many unanswered questions remain, e.g. how the distribution of individual BVOC compounds correlated with temperature and drought stress as well as along the vertical canopy gradient.
 "Untargeted metabolomics investigation of volatile compounds involved in the development of apple superficial scald by PTR-ToF-MS",
, Jul, 2014.
<p>The superficial scald is an important physiological disorder affecting apple fruit during postharvest storage. To date, the accumulation, and further oxidation, of α-farnesene was considered as the most probable cause for the development of this physiopathy. In order to perform a more broad investigation, a PTR-ToF–MS (proton transfer reaction—time of flight—mass spectrometry) was employed to monitor the volatile organic compounds (VOCs) production along with the progression of this disorder in fruit of “Granny Smith”, an apple variety known to be highly susceptible to scald. The untargeted metabolite investigation was performed on both skin and pulp, as well as comparing control versus treated tissues with 1-methylcyclopropene (1-MCP), an ethylene competitor widely used to prevent the development of this phenomenon. The rapid and non-destructive analysis of the VOC array carried out by PTR-ToF–MS identified three specific groups of metabolites in the skin, among which the 6-methyl-5-hepten-2-one (MHO) resulted significantly associated with the development of the superficial scald in apple. The results proposed in this work suggest the use of this novel equipment for an on-line monitoring of the VOCs released by the apple during the postharvest storage, as well as to use MHO as a possible biochemical marker for an early detection of the superficial scald symptoms.</p>
[Tani2009] "Uptake of aldehydes and ketones at typical indoor concentrations by houseplants",
Environmental science & technology
, vol. 43, no. 21: ACS Publications, pp. 8338–8343, 2009.
The uptake rates of low-molecular weight aldehydes and ketones by peace lily (Spathiphyllum clevelandii) and golden pothos (Epipremnum aureum) leaves at typical indoor ambient concentrations (101−102 ppbv) were determined. The C3−C6 aldehydes and C4−C6 ketones were taken up by the plant leaves, but the C3 ketone acetone was not. The uptake rate normalized to the ambient concentration Ca ranged from 7 to 19 mmol m−2 s−1 and from 2 to 7 mmol m−2 s−1 for the aldehydes and ketones, respectively. Longer-term fumigation results revealed that the total uptake amounts were 30−100 times as much as the amounts dissolved in the leaf, suggesting that volatile organic carbons are metabolized in the leaf and/or translocated through the petiole. The ratio of the intercellular concentration to the external (ambient) concentration (Ci/Ca) was significantly lower for most aldehydes than for most ketones. In particular, a linear unsaturated aldehyde, crotonaldehyde, had a Ci/Ca ratio of 0, probably because of its highest solubility in water.
[Tani2010] "Uptake of methacrolein and methyl vinyl ketone by tree saplings and implications for forest atmosphere",
Environmental science & technology
, vol. 44, no. 18: ACS Publications, pp. 7096–7101, 2010.
Methacrolein (MACR) and methyl vinyl ketone (MVK) are oxygenates produced from isoprene which is abundantly emitted by trees. The uptake rate of these compounds by leaves of three different Quercus species, Q. acutissima, Q. myrsinaefolia, and Q. phillyraeoides, at typical concentrations within a forest (several part per billion by volume) were determined. The rates of uptake of croton aldehyde (CA) and methyl ethyl ketone (MEK) were also investigated for comparison. The rates of uptake of the two aldehydes MACR and CA were found to be higher than those of the two ketones. In particular, the rate of MEK uptake for Q. myrsinaefolia was exceptionally low. The ratio of intercellular to fumigated concentrations, Ci/Ca, for MACR and CA was found to be low (0−0.24), while the ratio for the two ketones was 0.22−0.90. To evaluate the contribution of tree uptake as a sink for the two isoprene-oxygenates within the forest canopy, loss rates of the compounds due to uptake by trees and by reactions with hydroxyl radicals (OH radicals) and O3 were calculated. The loss rate by tree uptake was the highest, followed by the reaction with OH radicals, even at a high OH concentration (0.15 pptv) both for MACR and MVK, suggesting that tree uptake provides a significant sink.
[Kato2004] "Urban air measurements using PTR-MS in Tokyo area and comparison with GC-FID measurements",
International Journal of Mass Spectrometry
, vol. 235, no. 2: Elsevier, pp. 103–110, 2004.
Ambient air at a suburban area in Tokyo was measured by proton transfer reaction mass spectrometry (PTR-MS) and GC-FID simultaneously. Good correlations were obtained for hydrocarbon concentrations between GC-FID and PTR-MS, but concentrations differed by factor of 0.52–2.15, depending on the hydrocarbon. This shows that the calculated PTR-MS data needs to be corrected by standard gas measurements. Isoprene measured by PTR-MS is influenced by other species and the results of isoprene is not reliable at low concentration. Oxygenated volatile organic carbons showed higher concentrations during summer than in fall. This reflects the enhanced photochemical reactivity in summer. On the other hand, aromatic hydrocarbons, emitted mainly from car exhaust, did not show a difference between summer and fall. The ratios of aromatic hydrocarbons can be used as an indicator of photochemical reaction. Enhanced photochemical reactions were expected from these ratios during summer.
 "Urban flux measurements reveal a large pool of oxygenated volatile organic compound emissions",
Proceedings of the National Academy of Sciences
, pp. 201714715, jan, 2018.
<p>The exchange of nonmethane volatile organic compounds (NMVOC) at the surface–atmosphere interface is a fundamental constraint and important boundary condition for atmospheric chemistry and its effects on climate. Anthropogenic emissions are thought to account for about half of the NMVOC flux into the atmosphere of the Northern Hemisphere, yet their budget is considerably uncertain due to the scarcity of appropriate top-down constraints. Here we present direct flux measurements of NMVOCs based on the eddy covariance technique, showing that the contribution of typical urban emission sources is comprised of a surprisingly large portion of oxygenated NMVOC. These results suggest that typical urban NMVOC emission sources could be significantly higher than currently projected in air chemistry and climate models.</p>
[Pinggera2005] "Urinary acetonitrile concentrations correlate with recent smoking behaviour.",
, vol. 95, no. 3: Department of Urology, Medical University of Innsbruck, 6020 Innsbruck, Austria. Germar-Michael.Pinggera@uibk.ac.at, pp. 306–309, Feb, 2005.
To assess the concentration of acetonitrile (a saturated aliphatic nitrile) in the urine of habitual cigarette smokers and non-smokers, as exposure to smoke can be measured by monitoring ambient air or by in vivo tests, but acetonitrile measured in exhaled breath is reportedly a quantitative marker of recent smoking behaviour.The study included 101 volunteers (57 men and 44 women, mean age 49 years). An absence of urinary tract infection on urine analysis or clinical history was mandatory. The subjects were classified into five groups, i.e. a control group of non-smokers and four groups according to the number of cigarettes smoked daily. Urine samples were stored at 8 degrees C until acetonitrile was measured, within 24 h of collection, using proton-transfer reaction mass spectrometry (PTR-MS). Each measurement was repeated at least 10 times, and the mean used for statistical analysis.The mean (sd) acetonitrile level in the urine of 46 non-smokers was 3.74 (1.78) parts per billion volatile (ppbv). The concentration of acetonitrile increased with the number of cigarettes smoked daily, the highest concentration being in the subgroup of 13 very heavy smokers (>30 cigarettes/day) with means up to 28.04 (5.38) ppbv.PTR-MS is a quick, noninvasive online method for determining urinary acetonitrile levels, a marker for recent active and passive smoking behaviour, and thus for checking compliance. As smoking has been shown to affect the genesis of bladder cancer, further studies are required to determine the association of acetonitrile with bladder cancer.
[Agarwal2011] "Use of proton transfer reaction time-of-flight mass spectrometry for the analytical detection of illicit and controlled prescription drugs at room temperature via direct headspace sampling.",
Anal Bioanal Chem
, vol. 400, no. 8: sitaet Innsbruck, Innsbruck, Austria., pp. 2631–2639, Jun, 2011.
The first reported use of proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) for the detection of a range of illicit and prescribed drugs is presented here. We describe the capabilities of PTR-TOF-MS to detect the following commonly used narcotics-ecstasy (N-methyl-3,4-methylenedioxyamphetamine), morphine, codeine, cocaine and heroin-by the direct sampling of the headspace above small solid quantities (approximately 50 mg) of the drugs placed in glass vials at room temperature, i.e. with no heating of the sample and no pre-concentration. We demonstrate in this paper the ability to identify the drugs, both illicit and prescribed, using PTR-TOF-MS through the accurate m/z assignment of the protonated parent molecule to the second decimal place. We have also included in this study measurements with an impure sample of heroin, containing typical substances found in "street" heroin, to illustrate the use of the technology for more "real-world" samples. Therefore, in a real-world complex chemical environment, a high level of confidence can be placed on the detection of drugs. Although the protonated parent is observed for all drugs, the reactant channel leading to this species is not the only one observed and neither is it necessarily the most dominant. Details on the observed fragmentation behaviour are discussed and compared to electrospray ionisation MS(n) studies available in the literature.
[Karl2003a] "Use of proton-transfer-reaction mass spectrometry to characterize volatile organic compound sources at the La Porte super site during the Texas Air Quality Study 2000",
Journal of geophysical research
, vol. 108, no. D16: American Geophysical Union, pp. 4508, 2003.
Proton-transfer-reaction mass spectrometry (PTR-MS) was deployed for continuous real-time monitoring of volatile organic compounds (VOCs) at a site near the Houston Ship Channel during the Texas Air Quality Study 2000. Overall, 28 ions dominated the PTR-MS mass spectra and were assigned as anthropogenic aromatics (e.g., benzene, toluene, xylenes) and hydrocarbons (propene, isoprene), oxygenated compounds (e.g., formaldehyde, acetaldehyde, acetone, methanol, C7 carbonyls), and three nitrogen-containing compounds (e.g., HCN, acetonitrile and acrylonitrile). Biogenic VOCs were minor components at this site. Propene was the most abundant lightweight hydrocarbon detected by this technique with concentrations up to 100+ nmol mol−1, and was highly correlated with its oxidation products, formaldehyde (up to ∼40 nmol mol−1) and acetaldehyde (up to ∼80 nmol/mol), with typical ratios close to 1 in propene-dominated plumes. In the case of aromatic species the high time resolution of the obtained data set helped in identifying different anthropogenic sources (e.g., industrial from urban emissions) and testing current emission inventories. A comparison with results from complimentary techniques (gas chromatography, differential optical absorption spectroscopy) was used to assess the selectivity of this on-line technique in a complex urban and industrial VOC matrix and give an interpretation of mass scans obtained by “soft” chemical ionization using proton-transfer via H3O+. The method was especially valuable in monitoring rapidly changing VOC plumes which passed over the site, and when coupled with meteorological data it was possible to identify likely sources.
[Steele2011] "On the Use of SIFT-MS and PTR-MS Experiments to Explore Reaction Mechanisms in Plasmas of Volatile Organics: Siloxanes",
Plasma Processes and Polymers
, vol. 8, no. 4: Wiley Online Library, pp. 287–294, 2011.
Selected ion flow tube mass spectrometry (SIFT-MS) and proton transfer reaction mass spectrometry (PTR-MS) are used to explore ion-molecule reactions in low temperature and pressure plasmas of hexamethyldisiloxane. These techniques shed new light on possible reactions taking place within such plasma environments and validate many of the reaction pathways previously advocated based upon plasma-phase MS. However, SIFT-MS and PTR-MS results draw attention to the possible importance of the H3O+ ion in initiating the formation of oligomeric ions, a point previously missed in plasma-MS studies.
[Beauchamp2008] "On the use of Tedlar(R) bags for breath-gas sampling and analysis",
Journal of Breath Research
, vol. 2, no. 4, pp. 046001, 2008.
The storage capability of Tedlar(R) bags for gaseous compounds was assessed using on-line proton-transfer-reaction mass spectrometry (PTR-MS). Sample bags were filled with a mixture of volatile organic compounds (VOCs) at known quantities in the ppbv range. The test gas included alcohol, nitrile, aldehyde, ketone, terpene and aromatic compounds. PTR-MS enabled frequent bag-direct measurements of compound abundances over a 70 h storage period. Concentrations of all compounds decreased with bag storage time, with compound-specific decay rates. The most rapid decline in concentration levels was seen for water vapour in the bag, i.e. sample humidity. Such a decrease is particularly relevant for breath-gas samples, where water vapour content is high. Compound losses were attributed to a combination of adsorption to and diffusion through the bag walls. Storage property observations suggest that sample analyses made within 10 h of sampling offer adequate sample authenticity replication. Based on observations, an appropriate bag-cleaning procedure was established and assessed. Results indicated that acceptable bag cleanliness for breath-gas sampling is achievable.
[Vesin2012] "Use of the HS-PTR-MS for online measurements of pyrethroids during indoor insecticide treatments.",
Anal Bioanal Chem
, vol. 403, no. 7: Aix-Marseille Univ, LCE-IRA, 13331 Marseille, France., pp. 1907–1921, Jun, 2012.
A high-sensitivity proton transfer reaction mass spectrometer (HS-PTR-MS) has been used to study the temporal evolution of pesticide concentrations in indoor environments. Because of the high time variability of the indoor air concentrations during household pesticide applications, the use of this online high time resolution instrument is found relevant. Four pyrethroid pesticides of the latest generation that are commonly found in electric vaporizer refills, namely, transfluthrin, empenthrin, tetramethrin, and prallethrin, were considered. A controlled pesticide generation system was settled and coupled to a HS-PTR-MS analyzer, and a calibration procedure based on the fragmentation patterns of the protonated molecules was performed. To illustrate the functionality of the method, measurements of the concentration-time profiles of transfluthrin contained in an electric vaporizer were carried out in a full-scale environmental room under air exchange rate-controlled conditions. This study demonstrates that the HS-PTR-MS technique can provide online and high time-resolved measurements of semi-volatile organic compounds such as pyrethroid insecticides.
[Hellen2008] "Using proton transfer reaction mass spectrometry for online analysis of secondary organic aerosols.",
Environ Sci Technol
, vol. 42, no. 19: Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland. email@example.com, pp. 7347–7353, Oct, 2008.
Proton-transfer-reaction mass spectrometry (PTR-MS) is a useful tool in ambient trace gas analysis, especially for the analysis of oxygenated volatile organic compounds (OVOC). Many OVOCs are produced during photooxidation of volatile organic compounds and contribute to both the gas phase and secondary organic aerosols (SOA). The inlet system of the PTR-MS instrument was modified to allow also for the measurement of the particulate phase of an aerosol with a high time resolution. The new inlet consists mainly of a denuder to strip off the gas phase, and a heater (120/150 degrees C) to vaporize the aerosol particles. This inlet system was tested with pinonic acid particles generated with a nebulizer and SOA particles formed during the photooxidation of 1,3,5-trimethylbenzene and alpha-pinene with NO(x) in a smog chamber. The performance of this new technique is discussed and the partitioning coefficients for the oxidation products are estimated.