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[Oezdestan2013] Özdestan, Ö., S. M. van Ruth, M. Alewijn, A. Koot, A. Romano, L. Cappellin, and F. Biasioli, "Differentiation of specialty coffees by proton transfer reaction-mass spectrometry", Food Research International: Elsevier, 2013.
Link: http://www.sciencedirect.com/science/article/pii/S0963996913003025
Abstract
In the coffee sector a diversity of certifications is available, with the most well-known being organic and fair trade. Intrinsic markers of products may help to assure the authenticity of food products and complement administrative controls. In the present study 110 market coffees with special production traits were characterized by high sensitivity proton transfer reaction mass spectrometry (HS PTR-MS) and volatiles were tentatively identified by PTR-time of flight MS. Espresso coffees, Kopi Luwak coffee and organic coffees could be distinguished by their profiles of volatile compounds with the help of chemometrics. A PLS-DA classification model was estimated to classify the organic and regular coffees by their HS PTR-MS mass spectra. Cross validation showed correct prediction of 42 out of the 43 (98%) organic coffee samples and 63 out of the 67 (95%) regular coffee samples. Therefore, the presented strategy is a promising approach to rapid organic coffee authentication.
[Juerschik2010] Juerschik, S., A. Tani, P. Sulzer, S. Haidacher, A. Jordan, R. Schottkowsky, E. Hartungen, G. Hanel, H. Seehauser, L. Märk, et al., "Direct aqueous injection analysis of trace compounds in water with proton-transfer-reaction mass spectrometry (PTR-MS)", International Journal of Mass Spectrometry, vol. 289, no. 2: Elsevier, pp. 173–176, 2010.
Link: http://www.sciencedirect.com/science/article/pii/S1387380609003406
Abstract
Here we present proof-of-principle investigations on a novel inlet system for proton-transfer-reaction mass spectrometry (PTR-MS) that allows for the analysis of trace compounds dissolved in water. The PTR-MS technique offers many advantages, such as real-time analysis, online quantification, no need for sample preparation, very low detection limits, etc.; however it requires gas phase samples and therefore liquid samples cannot be investigated directly. Attempts to measure trace compounds in water that have been made so far are mainly headspace analysis above the water surface and membrane inlet setups, which both are well suitable for certain applications, but also suffer from significant disadvantages. The direct aqueous injection (DAI) technique which we will discuss here turns out to be an ideal solution for the analysis of liquid samples with PTR-MS. We show that we can detect trace compounds in water over several orders of magnitude down to a concentration level of about 100 pptw, while only consuming about 100 μl of the sample. The response time of the setup is about 20 s and can therefore definitely be called “online”. Moreover the method is applicable to the analysis of all substances and not limited by the permeability of a membrane.
[1492] Misztal, P.. K., E.. Nemitz, B.. Langford, C.. F. Di Marco, G.. J. Phillips, C.. N. Hewitt, A.. R. MacKenzie, S.. M. Owen, D.. Fowler, M.. R. Heal, et al., "Direct ecosystem fluxes of volatile organic compounds from oil palms in South-East Asia", Atmospheric Chemistry and Physics, vol. 11, pp. 8995–9017, 2011.
Link: http://www.atmos-chem-phys.net/11/8995/2011/
Abstract
<p>This paper reports the first direct eddy covariance fluxes of reactive biogenic volatile organic compounds (BVOCs) from oil palms to the atmosphere using proton-transfer-reaction mass spectrometry (PTR-MS), measured at a plantation in Malaysian Borneo. At midday, net isoprene flux constituted the largest fraction (84 %) of all emitted BVOCs measured, at up to 30 mg m&minus;2 h&minus;1 over 12 days. By contrast, the sum of its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) exhibited clear deposition of 1 mg m&minus;2 h&minus;1, with a small average canopy resistance of 230 s m&minus;1. Approximately 15 % of the resolved BVOC flux from oil palm trees could be attributed to floral emissions, which are thought to be the largest reported biogenic source of estragole and possibly also toluene. Although on average the midday volume mixing ratio of estragole exceeded that of toluene by almost a factor of two, the corresponding fluxes of these two compounds were nearly the same, amounting to 0.81 and 0.76 mg m&minus;2 h&minus;1, respectively. By fitting the canopy temperature and PAR response of the MEGAN emissions algorithm for isoprene and other emitted BVOCs a basal emission rate of isoprene of 7.8 mg m&minus;2 h&minus;1 was derived. We parameterise fluxes of depositing compounds using a resistance approach using direct canopy measurements of deposition. Consistent with Karl et al. (2010), we also propose that it is important to include deposition in flux models, especially for secondary oxidation products, in order to improve flux predictions.</p>
[Knighton2012] W Knighton, B., S. C. Herndon, J. F. Franklin, E. C. Wood, J. Wormhoudt, W. Brooks, E. C. Fortner, and D. T. Allen, "Direct measurement of volatile organic compound emissions from industrial flares using real-time online techniques: Proton Transfer Reaction Mass Spectrometry and Tunable Infrared Laser Differential Absorption Spectroscopy", Industrial & Engineering Chemistry Research, vol. 51, no. 39: ACS Publications, pp. 12674–12684, 2012.
Link: http://pubs.acs.org/doi/abs/10.1021/ie202695v
Abstract
During the 2010 Comprehensive Flare Study a suite of analytical instrumentation was employed to monitor and quantify in real-time the volatile organic compound (VOC) emissions emanating from an industrial chemical process flare burning either propene/natural gas or propane/natural gas. To our knowledge this represents the first time the VOC composition has been directly measured as a function of flare efficiency on an operational full-scale flare. This compositional information was obtained using a suite of proton-transfer-reaction mass spectrometers (PTR-MS) and quantum cascade laser tunable infrared differential absorption spectrometers (QCL-TILDAS) to measure the unburned fuel and associated combustion byproducts. Methane, ethyne, ethene, and formaldehyde were measured using the QC-TILDAS. Propene, acetaldehyde, methanol, benzene, acrolein, and the sum of the C3H6O isomers were measured with the PTR-MS. A second PTR-MS equipped with a gas chromatograph (GC) was operated in parallel and was used to verify the identity of the neutral components that were responsible for producing the ions monitored with the first PTR-MS. Additional components including 1,3-butadiene and C3H4 (propyne or allene) were identified using the GC/PTR-MS. The propene concentrations derived from the PTR-MS were found to agree with measurements made using a conventional GC with a flame ionization detector (FID). The VOC product (excludes fuel components) speciation profile is more dependent on fuel composition, propene versus propane, than on flare type, air-assisted versus steam-assisted, and is essentially constant with respect to combustion efficiency for combustion efficiencies >0.8. Propane flares produce more alkenes with ethene and propene accounting for approximately 80% (per carbon basis) of the VOC combustion product. The propene partial combustion product profile was observed to contain relatively more oxygenated material where formaldehyde and acetaldehyde are major contributors and account for 20 - 25% of VOC product carbon. Steam-assisted flares produce less ethyne and benzene than air-assisted flares. This observation is consistent with the understanding that steam assisted flares are more efficient at reducing soot, which is formed via the same reaction mechanisms that form benzene and ethyne.
[1833] Müller, M., P. Eichler, B. D'Anna, W. Tan, and A. Wisthaler, "Direct Sampling and Analysis of Atmospheric Particulate Organic Matter by Proton-Transfer-Reaction Mass Spectrometry", Analytical Chemistry, sep, 2017.
Link: http://pubs.acs.org/doi/10.1021/acs.analchem.7b02582
Abstract
<p>We report on a new method for analyzing atmospheric submicrometer particulate organic matter which combines direct particle sampling and volatilization with online chemical ionization mass spectrometric analysis. Technically, the method relies on the combined use of a CHARON (&ldquo;Chemical Analysis of Aerosol Online&rdquo;) particle inlet and a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS). Laboratory studies on target analytes showed that the ionization conditions in the PTR-ToF-MS lead to extensive fragmentation of levoglucosan and cis-pinonic acid, while protonated oleic acid and 5α-cholestane molecules remain intact. Potential problems and biases in quantitative and qualitative analyses are discussed. Side-by-side atmospheric comparison measurements of total particulate organic mass and levoglucosan with an aerosol mass spectrometer (AMS) were in good agreement. Complex and clearly distinct organic mass spectra were obtained from atmospheric measurements in three European cities (Lyon, Valencia, Innsbruck). Data visualization in reduced-parameter frameworks (e.g., oxidation state of carbon vs carbon number) revealed that the CHARON-PTR-ToF-MS technique adds significant analytical capabilities for characterizing particulate organic carbon in the Earth&rsquo;s atmosphere. Positive matrix factorization (PMF) was used for apportioning sources of atmospheric particles in late fall in Innsbruck. The m/z signatures of known source marker compounds (levoglucosan and resin acids, polycyclic aromatic hydrocarbons, nicotine) in the mass spectra were used to assign PMF factors to biomass burning, traffic, and smoking emission sources.</p>
[Biasioli2011] Biasioli, F., C. Yeretzian, T. D. Märk, J. Dewulf, and H. Van Langenhove, "Direct-injection mass spectrometry adds the time dimension to (B) VOC analysis", TrAC Trends in Analytical Chemistry, vol. 30, no. 7: Elsevier, pp. 1003–1017, 2011.
Link: http://www.sciencedirect.com/science/article/pii/S0165993611001269
Abstract
In the past decade, we have witnessed rapid development of direct-injection mass spectrometric (DIMS) technologies that combine ever-improving mass and time resolution with high sensitivity and robustness. Here, we review some of the most significant DIMS technologies, which have been applied to rapid monitoring and quantification of volatile organic compounds (VOCs) and biogenic VOCS (BVOCs). They include MS-e-noses, atmospheric-pressure chemical ionization (APCI), proton-transfer-reaction mass spectrometry (PTR-MS), and selected ion-flow-tube mass spectrometry (SIFT-MS). DIMS-based MS-e-noses provide the possibility to screen large sample sets and may yield rich analytical information. APCI is a widespread ionization method and pioneered DIMS in environmental and flavor-release applications. SIFT-MS and PTR-MS allow better control of precursor-ion generation and hence of the ionization process. SIFT-MS puts the focus on control of the ionization process, while PTR-MS does so on sensitivity. Most (B)VOCs of interest can be efficiently detected and often identified by DIMS, thanks also to the possibility of switching between different precursor ions and the recent realization of time-of-flight-based equipments. Finally, we give selected examples of applications for each of the key technologies, including research in food-quality control (MS-e-nose), flavor release (APCI), environmental sciences (PTR-MS) and health sciences (SIFT-MS).
[Brunner2010] Brunner, C.., W.. Szymczak, V.. Hoellriegl, S.. Moertl, H.. Oelmez, A.. Bergner, R.M.. Huber, C. Hoeschen, and U. Oeh, "Discrimination of cancerous and non-cancerous cell lines by headspace-analysis with PTR-MS", Analytical and Bioanalytical Chemistry, vol. 397: Springer-Verlag, pp. 2315-2324, 2010.
Link: http://dx.doi.org/10.1007/s00216-010-3838-x
Abstract
Proton transfer reaction mass spectrometry (PTR-MS) has been used to analyze the volatile organic compounds (VOCs) emitted by in-vitro cultured human cells. For this purpose, two pairs of cancerous and non-cancerous human cell lines were selected:1. lung epithelium cells A-549 and retinal pigment epithelium cells hTERT-RPE1, cultured in different growth media; and 2. squamous lung carcinoma cells EPLC and immortalized human bronchial epithelial cells BEAS2B, cultured in identical growth medium. The VOCs in the headspace of the cell cultures were sampled: 1. online by drawing off the gas directly from the culture flask; and 2. by accumulation of the VOCs in PTFE bags connected to the flask for at least 12 h. The pure media were analyzed in the same way as the corresponding cells in order to provide a reference. Direct comparison of headspace VOCs from flasks with cells plus medium and from flasks with pure medium enabled the characterization of cell-line-specific production or consumption of VOCs. Among all identified VOCs in this respect, the most outstanding compound was m/z?=?45 (acetaldehyde) revealing significant consumption by the cancerous cell lines but not by the non-cancerous cells. By applying multivariate statistical analysis using 42 selected marker VOCs, it was possible to clearly separate the cancerous and non-cancerous cell lines from each other.
[1586] Brunner, C.., W.. Szymczak, V.. Höllriegl, S.. Mörtl, H.. Oelmez, A.. Bergner, R.. M. Huber, C. Hoeschen, and U. Oeh, "Discrimination of cancerous and non-cancerous cell lines by headspace-analysis with PTR-MS.", Anal Bioanal Chem, vol. 397, pp. 2315–2324, Jul, 2010.
Link: http://dx.doi.org/10.1007/s00216-010-3838-x
Abstract
<p>Proton transfer reaction mass spectrometry (PTR-MS) has been used to analyze the volatile organic compounds (VOCs) emitted by in-vitro cultured human cells. For this purpose, two pairs of cancerous and non-cancerous human cell lines were selected:1. lung epithelium cells A-549 and retinal pigment epithelium cells hTERT-RPE1, cultured in different growth media; and 2. squamous lung carcinoma cells EPLC and immortalized human bronchial epithelial cells BEAS2B, cultured in identical growth medium. The VOCs in the headspace of the cell cultures were sampled: 1. online by drawing off the gas directly from the culture flask; and 2. by accumulation of the VOCs in PTFE bags connected to the flask for at least 12 h. The pure media were analyzed in the same way as the corresponding cells in order to provide a reference. Direct comparison of headspace VOCs from flasks with cells plus medium and from flasks with pure medium enabled the characterization of cell-line-specific production or consumption of VOCs. Among all identified VOCs in this respect, the most outstanding compound was m/z = 45 (acetaldehyde) revealing significant consumption by the cancerous cell lines but not by the non-cancerous cells. By applying multivariate statistical analysis using 42 selected marker VOCs, it was possible to clearly separate the cancerous and non-cancerous cell lines from each other.</p>
[Ciesa2013] Ciesa, F., J. Dalla Via, A. Wisthaler, A. Zanella, W. Guerra, T. Mikoviny, T. D. Märk, and M. Oberhuber, "Discrimination of four different postharvest treatments of ‘Red Delicious’ apples based on their volatile organic compound (VOC) emissions during shelf-life measured by proton transfer reaction mass spectrometry (PTR-MS)", Postharvest Biology and Technology, vol. 86, pp. 329 - 336, 2013.
Link: http://www.sciencedirect.com/science/article/pii/S0925521413002032
Abstract
Abstract Storage methods extend the postharvest life of apples from weeks to up to one year; however, these methods also alter the production of volatile organic compounds (VOCs), which amongst others, are important for aroma attributes. While the impact of storage on particular aroma components has been established, high throughput methods for determining the storage history during shelf-life are elusive. Here we show the potential of proton transfer reaction-mass spectrometry (PTR-MS), an MS-based metabolic fingerprinting technique, for characterizing fruit in the postharvest chain. The \{VOC\} fingerprint of apples (Malus&#xa0;×&#xa0;domestica Borkh. ‘Red Delicious’) was analyzed by PTR-MS during four weeks of shelf-life ripening after storage under four different storage conditions: \{ULO\} (ultra-low oxygen), DCA-CF (dynamic controlled atmosphere monitored by chlorophyll fluorescence), \{RLOS\} (repeated low oxygen stress) and 1-MCP (1-methylcyclopropene) in ULO. \{PTR\} fingerprint mass spectra of the apple headspace, obtained in short time without sample preparation or preconcentration, were sufficient to discriminate the four storage conditions during shelf-life. Moreover, we were able to monitor the changes in quality-critical \{VOC\} classes, including esters and terpenes, during shelf-life and observe the differential impact of the storage history on these VOCs. This work emphasizes the potential of PTR-MS as a valuable addition to targeted GC–MS-based approaches in postharvest research.
[LaPorta2004] La Porta, N., F. Biasioli, F. Gasperi, and T. D. Märk, "Discrimination of Heterobasidion annosum ISGs by evaluation of volatile organic compounds", S. Michele all'Adige, Italy, vol. 27, no. 8, pp. 379–382, 2004.
Link: http://core.kmi.open.ac.uk/download/pdf/2835560#page=418
Abstract
Heterobasidion annosum represents one of the most dangerous fungi in the conifer forest of the boreal hemisphere. This fungus was differentiated into three biological species (Intersterile groups; ISGs) characterized by different host specificity, patogenicity and distribution. A fast and easy identification of the ISG has important consequences on the silvicultural decition making. However, the determination of the ISG from the morphological traits of fruit bodies or, least of all, from mycelium is usually not easy. Proton Transfer Reaction – Mass Spectrometry (PTR-MS) is a new technique proposed and realised by the University of Innsbruck, and now issued also to the market. This technique allows high performance on-line measurements for a large number of VOCs. The aim of this work was to verify the possibility to discriminate the H. annosum ISGs based on their volatile compound emission and to identify putative characteristic masses that may play an important role in the host specificity and in the specific antagonistic fungi among each ISGs. Twelve strains belong to the three ISGs (here idicated by F, P and S) were analysed by PTRMS fingerprinting. P ISG was definitely separated from F and S ISGs. In addition, several masses show to be significantly different among the three ISGs. ANOVA on PTR-MS peak values identified 16 significant masses out of 230. Applications and limitations of this approach are discussed.
[1635] Kus, P. Marek, and S. van Ruth, "Discrimination of Polish unifloral honeys using overall PTR-{MS} and HPLC fingerprints combined with chemometrics", LWT - Food Science and Technology, vol. 62, pp. 69–75, Jun, 2015.
Link: http://dx.doi.org/10.1016/j.lwt.2014.12.060
Abstract
<p>A total of 62 honey samples of six floral origins (rapeseed, lime, heather, cornflower, buckwheat and black locust) were analysed by means of proton transfer reaction mass spectrometry (PTR-MS) and HPLCDAD. The data were evaluated by principal component analysis and k-nearest neighbours classification in order to examine consistent differences in analytical fingerprints between various honeys allowing their discrimination. The study revealed, that both techniques were able to distinguish the floral origins, however the HPLC shows advantage over PTR-MS providing substantially better differentiation of all analysed honey types. Especially HPLC fingerprints recorded at 210 nm were most suitable for discrimination of botanical origin with the use of chemometric analysis. The obtained classification rates were: 100%, 93%, 100%, 83%, 100%, 100% (HPLC) and 69%, 67%, 78%, 67%, 100%, 88% (PTR-MS) for rapeseed, lime, heather, cornflower, buckwheat and black locust, respectively. Even if performance of PTR-MS in general was lower than HPLC, it might be useful for fast on-line screening of buckwheat honey.</p>
[Grabmer2004] Grabmer, W., M. Graus, C. Lindinger, A. Wisthaler, B. Rappenglück, R. Steinbrecher, and A. Hansel, "Disjunct eddy covariance measurements of monoterpene fluxes from a Norway spruce forest using PTR-MS", International Journal of Mass Spectrometry, vol. 239, no. 2: Elsevier, pp. 111–115, 2004.
Link: http://www.sciencedirect.com/science/article/pii/S1387380604003914
Abstract
Interest in reliable quantification of organic trace compounds released from terrestrial ecosystems stems from their impact on oxidant levels such as ozone and hydroxyl radicals and on secondary organic aerosol formation. In an attempt to quantify these emissions, a disjunct sampler (DS) was coupled to a PTR-MS instrument. In the disjunct eddy covariance (DEC) technique, an instantaneous grab sample is taken at intervals of tens of seconds and vertical wind speed is recorded at the instant of sample collection. The intermittent periods are used for sample analysis by a moderately fast chemical sensor, in this case a PTR-MS instrument, which allows for fast and sensitive detection of biogenic volatile organic compounds. The vertical turbulent transport of a trace compound is then calculated from the covariance of the fluctuations in vertical wind speed and compound mixing ratio. Fluxes of monoterpenes from a Norway spruce forest were measured during the 2002 summer intensive field campaign of BEWA2000 and results compared well with data obtained using relaxed eddy accumulation (REA) and the enclosure approach. In addition to this field experiment, a laboratory test was carried out to validate the disjunct sampling procedure.
[Warneke2002] Warneke, C., SL. Luxembourg, JA. De Gouw, HJI. Rinne, AB. Guenther, and R. Fall, "Disjunct eddy covariance measurements of oxygenated volatile organic compounds fluxes from an alfalfa field before and after cutting", Journal of geophysical research, vol. 107, no. D8: American Geophysical Union, pp. 4067, 2002.
Link: http://onlinelibrary.wiley.com/doi/10.1029/2001JD000594/abstract
Abstract
[1] There is interest in and significant uncertainty about the emissions of oxygenated volatile organic compounds (oxVOCs) from vegetation to the atmosphere. Here, we measured the fluxes of selected oxVOCs from an alfalfa field, before, during, and after cutting, using a combination of disjunct eddy covariance and proton-transfer-reaction mass spectrometry. Over the course of 1 day a significant methanol flux of 4 mg m−2 h−1 was observed from undisturbed alfalfa with a maximum at 0800 LT, possibly caused by the evaporation of dew. A smaller release of hexenals during this day (0.04 mg m−2 h−1) demonstrated the sensitivity of the method. Other results suggested that acetaldehyde and acetone were released in the afternoon but were lost by dry deposition in the evening and morning; deposition velocities were estimated to be 0.2 cm s−1 (acetaldehyde) and 0.09 cm s−1 (acetone). After the alfalfa was cut the emissions of methanol, acetaldehyde, acetone, and hexenals were significantly enhanced and remained high for three days during which the alfalfa was drying. After a rainstorm the oxVOC emissions from the cut, wet alfalfa increased even more. Nighttime measurements yielded low oxVOC fluxes in general, but the high variability of the concentrations during the night and the high degree of correlation between different oxVOCs suggest that the nighttime releases of oxVOCs from alfalfa were nonzero. This work suggests that the global source of oxVOCs due to the production of hay is of minor importance. The emission flux of methanol from vegetation during the growing season may be very large on a global basis.
[Rinne2001] Rinne, HJI., AB. Guenther, C. Warneke, JA. De Gouw, and SL. Luxembourg, "Disjunct eddy covariance technique for trace gas flux measurements", Geophysical Research Letters, vol. 28, no. 16, pp. 3139–3142, 2001.
Link: http://www.agu.org/journals/gl/gl0116/2001GL012900/pdf/2001GL012900.pdf
[Lanza2013] Lanza, M., J. W. Acton, S. Jürschik, P. Sulzer, K. Breiev, A. Jordan, E. Hartungen, G. Hanel, L. Märk, C. A. Mayhew, et al., "Distinguishing two isomeric mephedrone substitutes with selective reagent ionisation mass spectrometry (SRI-MS)", Journal of Mass Spectrometry, vol. 48, no. 9, pp. 1015–1018, 2013.
Link: http://dx.doi.org/10.1002/jms.3253
Abstract
The isomers 4-methylethcathinone and N-ethylbuphedrone are substitutes for the recently banned drug mephedrone. We find that with conventional proton transfer reaction mass spectrometry (PTR-MS), it is not possible to distinguish between these two isomers, because essentially for both substances, only the protonated molecules are observed at a mass-to-charge ratio of 192 (C12H18NO+). However, when utilising an advanced PTR-MS instrument that allows us to switch the reagent ions (selective reagent ionisation) from H3O+ (which is commonly used in PTR-MS) to NO+, O2+ and Kr+, characteristic product (fragment) ions are detected: C4H10N+ (72 Da) for 4-methylethcathinone and C5H12N+ (86 Da) for N-ethylbuphedrone; thus, selective reagent ionisation MS proves to be a powerful tool for fast detection and identification of these compounds. Copyright © 2013 John Wiley & Sons, Ltd.
[Velasco2007] Velasco, E., B. Lamb, H. Westberg, E. Allwine, G. Sosa, JL. Arriaga-Colina, BT. Jobson, L. M Alexander, P. Prazeller, W. B. Knighton, et al., "Distribution, magnitudes, reactivities, ratios and diurnal patterns of volatile organic compounds in the Valley of Mexico during the MCMA 2002 & 2003 field campaigns", Atmospheric Chemistry and Physics, vol. 7, no. 2: Copernicus GmbH, pp. 329–353, 2007.
Link: http://www.atmos-chem-phys.net/7/329/2007/acp-7-329-2007.html
Abstract
A wide array of volatile organic compound (VOC) measurements was conducted in the Valley of Mexico during the MCMA-2002 and 2003 field campaigns. Study sites included locations in the urban core, in a heavily industrial area and at boundary sites in rural landscapes. In addition, a novel mobile-laboratory-based conditional sampling method was used to collect samples dominated by fresh on-road vehicle exhaust to identify those VOCs whose ambient concentrations were primarily due to vehicle emissions. Four distinct analytical techniques were used: whole air canister samples with Gas Chromatography/Flame Ionization Detection (GC-FID), on-line chemical ionization using a Proton Transfer Reaction Mass Spectrometer (PTR-MS), continuous real-time detection of olefins using a Fast Olefin Sensor (FOS), and long path measurements using UV Differential Optical Absorption Spectrometers (DOAS). The simultaneous use of these techniques provided a wide range of individual VOC measurements with different spatial and temporal scales. The VOC data were analyzed to understand concentration and spatial distributions, diurnal patterns, origin and reactivity in the atmosphere of Mexico City. The VOC burden (in ppbC) was dominated by alkanes (60%), followed by aromatics (15%) and olefins (5%). The remaining 20% was a mix of alkynes, halogenated hydrocarbons, oxygenated species (esters, ethers, etc.) and other unidentified VOCs. However, in terms of ozone production, olefins were the most relevant hydrocarbons. Elevated levels of toxic hydrocarbons, such as 1,3-butadiene, benzene, toluene and xylenes, were also observed. Results from these various analytical techniques showed that vehicle exhaust is the main source of VOCs in Mexico City and that diurnal patterns depend on vehicular traffic in addition to meteorological processes. Finally, examination of the VOC data in terms of lumped modeling VOC classes and its comparison to the VOC lumped emissions reported in other photochemical air quality modeling studies suggests that some alkanes are underestimated in the emissions inventory, while some olefins and aromatics are overestimated.
[1681] Pallozzi, E., G. Guidolotti, P. Ciccioli, F. Brilli, S. Feil, and C. Calfapietra, "Does the novel fast-GC coupled with PTR-TOF-MS allow a significant advancement in detecting VOC emissions from plants?", Agricultural and Forest Meteorology, vol. 216, pp. 232–240, Jan, 2016.
Link: http://dx.doi.org/10.1016/j.agrformet.2015.10.016
Abstract
<p>Most plants produce and emit a wide blend of biogenic volatile organic compounds (BVOCs). Among them, many isoprenoids exhibit a high atmospheric reactivity toward OH radicals and ozone. In the last few years, Proton Transfer Reaction&ndash;Mass Spectrometry (PTR&ndash;MS) has been widely used in both field and laboratory determination of BVOCs, complementing the traditional methods using gas chromatography&ndash;mass spectrometry (GC&ndash;MS) for their identification in air and emission sources. This technical note reports a number of experiments carried out with a PTR- (Time-of-Flight) TOF-MS equipped with a prototype fast-GC system, allowing a fast separation of those isobaric isoprenoid compounds that cannot be identified by a direct PTR-TOF-MS analysis. The potential of this fast-GC system to adequately complement the information provided by PTR-TOF-MS was investigated by using the BVOC emissions of Quercus ilex and Eucalyptus camaldulensis as reliable testing systems, due to the different blend of isoprenoid compounds emitted and the different dependence of their emission from environmental parameters. While the oak species is a strong monoterpene emitter, the eucalyptus used is one of the few plant species emitting both isoprene and monoterpenes. The performances provided by the type of fast-GC used in the new PTR-TOF-MS instrument were also compared with those afforded by conventional GC&ndash;MS methods. The results obtained in this investigation showed that this new instrument is indeed a quick and handy tool to determine the contribution of isoprene and eucalyptol to m/z 69.070 and monoterpenes and (Z)-3-hexenal to m/z 81.070, integrating well the on-line information provided by PTR-TOF-MS. However, some limitations emerged in the instrument as compared to traditional GC&ndash;MS, which can only be solved by implementing the injection and separation processes.</p>
[Kamysek2011] Kamysek, S., P. Fuchs, H. Schwoebel, J. P. Roesner, S. Kischkel, K. Wolter, C. Loeseken, J. K. Schubert, and W. Miekisch, "Drug detection in breath: effects of pulmonary blood flow and cardiac output on propofol exhalation.", Anal Bioanal Chem, vol. 401, no. 7: Department of Anesthesiology and Intensive Care, University of Rostock, Schillingallee 35, 18057 Rostock, Germany., pp. 2093–2102, Oct, 2011.
Link: http://dx.doi.org/10.1007/s00216-011-5099-8
Abstract
Breath analysis could offer a non-invasive means of intravenous drug monitoring if robust correlations between drug concentrations in breath and blood can be established. In this study, propofol blood and breath concentrations were determined in an animal model under varying physiological conditions. Propofol concentrations in breath were determined by means of two independently calibrated analytical methods: continuous, real-time proton transfer reaction mass spectrometry (PTR-MS) and discontinuous solid-phase micro-extraction coupled with gas chromatography mass spectrometry (SPME-GC-MS). Blood concentrations were determined by means of SPME-GC-MS. Effects of changes in pulmonary blood flow resulting in a decreased cardiac output (CO) and effects of dobutamine administration resulting in an increased CO on propofol breath concentrations and on the correlation between propofol blood and breath concentrations were investigated in seven acutely instrumented pigs. Discontinuous propofol determination in breath by means of alveolar sampling and SPME-GC-MS showed good agreement (R(2)=0.959) with continuous alveolar real-time measurement by means of PTR-MS. In all investigated animals, increasing cardiac output led to a deterioration of the relationship between breath and blood propofol concentrations (R(2)=0.783 for gas chromatography-mass spectrometry and R(2)=0.795 for PTR-MS). Decreasing pulmonary blood flow and cardiac output through banding of the pulmonary artery did not significantly affect the relationship between propofol breath and blood concentrations (R(2)>0.90). Estimation of propofol blood concentrations from exhaled alveolar concentrations seems possible by means of different analytical methods even when cardiac output is decreased. Increases in cardiac output preclude prediction of blood propofol concentration from exhaled concentrations.
[Singer2007] Singer, W.., J.. Beauchamp, J.. Herbig, J.. Dunkl, I.. Kohl, and A.. Hansel, "Dynamic Gas Dilution System for Accurate Calibration of Analytical Instruments such as PTR-MS", 3rd International PTR-MS Conference on Proton Transfer Reaction Mass Spectrometry and Its Applications, pp. 232-237, 2007.
Link: http://www.ionicon.com/sites/default/files/uploads/doc/contributions_ptr_ms_Conference_3.pdf
[Karl2003] Karl, T., C. Yeretzian, A. Jordan, and W. Lindinger, "Dynamic measurements of partition coefficients using proton-transfer-reaction mass spectrometry (PTR–MS)", International Journal of Mass Spectrometry, vol. 223: Elsevier, pp. 383–395, 2003.
Link: http://www.sciencedirect.com/science/article/pii/S1387380602009272
Abstract
Liquid–gas partition coefficients (HLC) of volatile organic compounds (VOCs) in water–air systems are determined using a novel dynamic approach by coupling a stripping cell directly to a proton-transfer-reaction mass spectrometer (PTR–MS). Two complementary set-ups are evaluated, one suited for determining HLCs of highly volatile compounds (<10 M/atm), the second adapted for medium to low volatile compounds (∼10–1000 M/atm). We validated the method using 2-butanone, investigated the temperature dependence of various HLCs and applied the stripping technique to a series of VOCs. Compared to alternative state-of-the-art techniques the present approach has the advantage of being simple, fast and less prone to artefacts. Furthermore, it allows to quantify volatile compounds in the headspace without calibration or addition of standards.
[King2010] King, J.., P.. Mochalski, A.. Kupferthaler, K.. Unterkofler, H.. Koc, W.. Filipiak, S.. Teschl, H.. Hinterhuber, and A.. Amann, "Dynamic profiles of volatile organic compounds in exhaled breath as determined by a coupled PTR-MS/GC-MS study.", Physiol Meas, vol. 31, no. 9: University Clinic for Anesthesia, Innsbruck Medical University, Anichstr. 35, A-6020 Innsbruck, Austria., pp. 1169–1184, Sep, 2010.
Link: http://dx.doi.org/10.1088/0967-3334/31/9/008
Abstract
In this phenomenological study we focus on dynamic measurements of volatile organic compounds (VOCs) in exhaled breath under exercise conditions. An experimental setup efficiently combining breath-by-breath analyses using proton transfer reaction mass spectrometry (PTR-MS) with data reflecting the behaviour of major hemodynamic and respiratory parameters is presented. Furthermore, a methodology for complementing continuous VOC profiles obtained by PTR-MS with simultaneous SPME/GC-MS measurements is outlined. These investigations aim at evaluating the impact of breathing patterns, cardiac output or blood pressure on the observed breath concentration and allow for the detection and identification of several VOCs revealing characteristic rest-to-work transitions in response to variations in ventilation or perfusion. Examples of such compounds include isoprene, methyl acetate, butane, DMS and 2-pentanone. In particular, both isoprene and methyl acetate exhibit a drastic rise in concentration shortly after the onset of exercise, usually by a factor of about 3-5 within approximately 1 min of pedalling. These specific VOCs might also be interpreted as potentially sensitive indicators for fluctuations of blood or respiratory flow and can therefore be viewed as candidate compounds for future assessments of hemodynamics, pulmonary function and gas exchange patterns via observed VOC behaviour.
[Deleris2011a] Déléris, I., A. Saint-Eve, F. Dakowski, E. Sémon, J-L. Le Quéré, H. Guillemin, and I. Souchon, "The dynamics of aroma release during consumption of candies of different structures, and relationship with temporal perception", Food Chemistry, vol. 127, no. 4: Elsevier, pp. 1615–1624, 2011.
Link: http://www.sciencedirect.com/science/article/pii/S0308814611002858
Abstract
We investigated the role of both candy texture and eating technique (melting or chewing) on the dynamics of aroma release. One novelty of this type of analysis was the simultaneous application of instrumental and sensory analysis. Four candy textures were established based on their storage modulus at 1 Hz by varying the gelatine content between 0 and 15% w/w. The invivo release of three aroma compounds was monitored using Proton Transfer Reaction Mass Spectrometry and with a trained panel of testers. The gelatine content had no significant effect on the headspace/product partition and diffusion properties of the aroma compounds. The highest invivo release for all aroma compounds was obtained with the 2% gelatine sample. Our findings indicated that aroma release was determined by interaction between the product properties and oral behaviour. Relations between the dynamics of release and perception (method of Temporal Dominance of Sensations) have been established on temporal parameters.
E
[1760] Seco, R., T. Karl, A. Guenther, K. P. Hosman, S. G. Pallardy, L. Gu, C. Geron, P. Harley, and S. Kim, "Ecosystem-scale volatile organic compound fluxes duringᅡᅠan extreme drought in a broadleaf temperate forestᅡᅠof the Missouri Ozarks (central USA)", Global Change Biology, vol. 21, pp. 3657–3674, Jul, 2015.
Link: http://dx.doi.org/10.1111/gcb.12980
Abstract
<p>Considerable amounts and varieties of biogenic volatile organic compounds (BVOCs) are exchanged between vegetation and the surrounding air. These BVOCs play key ecological and atmospheric roles that must be adequately represented for accurately modeling the coupled biosphere-atmosphere-climate earth system. One key uncertainty in existing models is the response of BVOC fluxes to an important global change process: drought. We describe the diurnal and seasonal variation in isoprene, monoterpene, and methanol fluxes from a temperate forest ecosystem before, during, and after an extreme 2012 drought event in the Ozark region of the central USA. BVOC fluxes were dominated by isoprene, which attained high emission rates of up to 35.4 mg m(-2) h(-1) at midday. Methanol fluxes were characterized by net deposition in the morning, changing to a net emission flux through the rest of the daylight hours. Net flux of CO2 reached its seasonal maximum approximately a month earlier than isoprenoid fluxes, which highlights the differential response of photosynthesis and isoprenoid emissions to progressing drought conditions. Nevertheless, both processes were strongly suppressed under extreme drought, although isoprene fluxes remained relatively high compared to reported fluxes from other ecosystems. Methanol exchange was less affected by drought throughout the season, confirming the complex processes driving biogenic methanol fluxes. The fraction of daytime (7-17 h) assimilated carbon released back to the atmosphere combining the three BVOCs measured was 2% of gross primary productivity (GPP) and 4.9% of net ecosystem exchange (NEE) on average for our whole measurement campaign, while exceeding 5% of GPP and 10% of NEE just before the strongest drought phase. The meganv2.1 model correctly predicted diurnal variations in fluxes driven mainly by light and temperature, although further research is needed to address model BVOC fluxes during drought events.</p>
[1512] Park, J.-H.., A.. H. Goldstein, J.. Timkovsky, S.. Fares, R.. Weber, J.. Karlik, and R.. Holzinger, "Eddy covariance emission and deposition flux measurements using proton transfer reaction-time of flight-mass spectrometry (PTR-TOF-{MS}): comparison with PTR-{MS} measured vertical gradients and fluxes", Atmospheric Chemistry and Physics Discussions, vol. 12, pp. 20435–20482, Aug, 2012.
Link: http://dx.doi.org/10.5194/acpd-12-20435-2012
Abstract
<p>During summer 2010, a proton transfer reaction-time of flight-mass spectrometer (PTR-TOF-MS) and a standard proton transfer reaction mass spectrometer (PTR-MS) were deployed simultaneously for one month in an orange orchard in the Central Valley of California to collect continuous data suitable for eddy covariance (EC) flux calculations. The high time resolution (5 Hz) and high mass resolution (up to 5000 m Δ m&minus;1) data from the PTR-TOF-MS provided the basis for calculating the concentration and flux for a wide range of volatile organic compounds (VOC). Throughout the campaign, 664 mass peaks were detected in mass-to-charge ratios between 10 and 1278. Here we present PTR-TOF-MS EC fluxes of the 27 ion species for which the vertical gradient was simultaneously measured by PTR-MS. These EC flux data were validated through spectral analysis (i.e. co-spectrum, normalized co-spectrum, and ogive). Based on inter-comparison of the two PTR instruments, no significant instrumental biases were found in either mixing ratios or fluxes, and the data showed agreement within 5% on average for methanol and acetone. For the measured biogenic volatile organic compounds (BVOC), the EC fluxes from PTR-TOF-MS were in agreement with the qualitatively inferred flux directions from vertical gradient measurements by PTR-MS. For the 27 selected ion species reported here, the PTR-TOF-MS measured total (24 h) mean net flux of 299 μg C m&minus;2 h&minus;1. The dominant BVOC emissions from this site were monoterpenes (m/z 81.070 + m/z 137.131 + m/z 95.086, 34%, 102 μg C m&minus;2 h&minus;1) and methanol (m/z 33.032, 18%, 72 μg C m&minus;2 h&minus;1). The next largest fluxes were detected at the following masses (attribution in parenthesis): m/z 59.048 (mostly acetone, 12.2%, 36.5 μg C m&minus;2 h&minus;1), m/z 61.027 (mostly acetic acid, 11.9%, 35.7 μg C m&minus;2 h&minus;1), m/z 93.069 (para-cymene + toluene, 4.1%, 12.2 μg C m&minus;2 h&minus;1), m/z 45.033 (acetaldehyde, 3.8%, 11.5 μg C m&minus;2 h&minus;1), m/z 71.048 (methylvinylketone + methacrolein, 2.4%, 7.1 μg C m&minus;2 h&minus;1), and m/z 69.071 (isoprene + 2-methyl-3-butene-2-ol, 1.8%, 5.3 μg C m&minus;2 h&minus;1). Low levels of emission and/or deposition (&lt;1.6% for each, 5.8% in total flux) were observed for the additional reported masses. Overall, our results show that EC flux measurements using PTR-TOF-MS is a powerful new tool for characterizing the biosphere-atmosphere exchange including both emission and deposition for a large range of BVOC and their oxidation products.</p>
[Spirig2005] Spirig, C., A. Neftel, C. Ammann, J. Dommen, W. Grabmer, A. Thielmann, A. Schaub, J. Beauchamp, A. Wisthaler, A. Hansel, et al., "Eddy covariance flux measurements of biogenic VOCs during ECHO 2003 using proton transfer reaction mass spectrometry", Atmospheric Chemistry and Physics, vol. 5, no. 2, pp. 465–481, 2005.
Link: http://hal.archives-ouvertes.fr/hal-00295614/
Abstract
Within the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. The eddy covariance (EC) technique was applied since it represents the most direct flux measurement approach on the canopy scale and is, therefore, least susceptible to these non-ideal conditions. A specific flux calculation method was used to account for the sequential multi-component PTR-MS measurements and allowing an individual delay time adjustment as well as a rigorous quality control based on cospectral analysis. The validated flux results are consistent with light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average daytime emissions of 0.94 and 0.3µg m-2s-1, respectively. Emissions of methanol reached on average 0.087µg m-2s-1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement.

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Selected PTR-MS related Reviews

F. Biasioli, C. Yeretzian, F. Gasperi, T. D. Märk: PTR-MS monitoring of VOCs and BVOCs in food science and technology, Trends in Analytical Chemistry 30 (7) (2011).
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J. de Gouw, C. Warneke, T. Karl, G. Eerdekens, C. van der Veen, R. Fall: Measurement of Volatile Organic Compounds in the Earth's Atmosphere using Proton-Transfer-Reaction Mass Spectrometry. Mass Spectrometry Reviews, 26 (2007), 223-257.
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W. Lindinger, A. Hansel, A. Jordan: Proton-transfer-reaction mass spectrometry (PTR–MS): on-line monitoring of volatile organic compounds at pptv levels, Chem. Soc. Rev. 27 (1998), 347-375.
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Lists with PTR-MS relevant publications of the University of Innsbruck can be found here: Atmospheric and indoor air chemistry, IMR, Environmental Physics and Nano-Bio-Physics

 

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