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| '''Proton-transfer-reaction mass spectrometry''' (PTR-MS) is a very sensitive technique for online monitoring of [[Volatile organic compound|volatile organic compounds (VOCs)]] in ambient air developed by scientists at the Institut für Ionenphysik at the [[University of Innsbruck|Leopold-Franzens University in Innsbruck]], Austria.<ref>A. Hansel, A. Jordan, R. Holzinger, P. Prazeller W. Vogel, W. Lindinger, Proton transfer reaction mass spectrometry: on-line trace gas analysis at ppb level, ''Int. J. of Mass Spectrom. and Ion Proc.'', 149/150, 609-619 ('''1995''').</ref>
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| A PTR-MS instrument consists of an [[ion source]] that is directly connected to a drift tube (in contrast to [[Selected ion flow tube mass spectrometry|SIFT-MS]] no mass filter is interconnected) and an analyzing system ([[quadrupole mass analyzer]] or [[time-of-flight mass spectrometer]]). Commercially available PTR-MS instruments have a [[Response time (technology)|response time]] of about 100 ms and reach a [[detection limit]] in the single digit [[Parts-per notation|pptv]] region. Established fields of application are environmental research, food and flavour science, biological research, medicine, etc.<ref name="ptrmsHP">[http://www.ionicon.com/documentation/publications.html Ionicon PTR-MS Scientific Publications - PTR-MS Bibliography<!-- Bot generated title -->]</ref><ref name="uibkHP">[http://www.uibk.ac.at/ionen-angewandte-physik/umwelt/publications/index.html.en Publications – University of Innsbruck<!-- Bot generated title -->]</ref>
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| == Theory == | |
| With [[Hydronium|H<sub>3</sub>O<sup>+</sup>]] as the primary ion the proton transfer process is (with <math>R</math> being the trace component)
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| :<math>H_3O^+ + R \longrightarrow RH^+ + H_2O</math> (1).
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| [[File:Evolution of ptr sensitivities.PNG|thumb|Fig. 1: Evolution of reagent ion yields and sensitivities of PTR-MS instruments taken from peer reviewed journal articles]]
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| Reaction (1) is only possible if energetically allowed, i.e. if the [[proton affinity]] of <math>R</math> is higher than the proton affinity of [[Water (molecule)|H<sub>2</sub>O]] (691 kJ/mol<ref>R.S. Blake, P.S. Monks, A.M. Ellis, Proton-Transfer Reaction Mass Spectrometry, ''Chem. Rev.'', 109, 861-896 ('''2009''')</ref>). As most components of [[Earth's atmosphere|ambient air]] possess a lower proton affinity than H<sub>2</sub>O (e.g. [[Nitrogen|N<sub>2</sub>]], [[Oxygen|O<sub>2</sub>]], [[Argon|Ar]], [[Carbon dioxide|CO<sub>2</sub>]], etc.) the H<sub>3</sub>O<sup>+</sup> ions only reacts with VOC trace components and the air itself acts as a [[buffer gas]]. Moreover due to the low number of trace components one can assume that the total number of H<sub>3</sub>O<sup>+</sup> ions remains nearly unchanged, which leads to the equation<ref name="Lindinger">W. Lindinger, A. Hansel and A. Jordan, On-line monitoring of volatile organic compounds at pptv levels by means of Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS): Medical applications, food control and environmental research, Review paper, ''Int. J. Mass Spectrom. Ion Proc.'', 173, 191-241 ('''1998''').</ref>
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| :<math>\lbrack RH^+\rbrack = \lbrack H_3O^+\rbrack_0 \left (1-e^{-k\lbrack R\rbrack t}\right )\approx \lbrack H_3O^+\rbrack _0 \lbrack R\rbrack kt</math> (2).
| |
| In equation (2) <math>\lbrack RH^+\rbrack</math> is the density of product ions, <math>\lbrack H_3O^+\rbrack_0</math> is the density of primary ions in absence of reactant molecules in the buffer gas, <math>k</math> is the [[reaction rate constant]] and <math>t</math> is the average time the ions need to pass the reaction region. With a PTR-MS instrument the number of product and of primary ions can be measured, the reaction rate constant can be found in literature for most substances<ref>Y. Ikezoe, S. Matsuoka and A. Viggiano, Gas Phase Ion-Molecule Reaction Rate Constants through 1986, ''Maruzen Company Ltd.'', Tokyo, ('''1987''').</ref> and the reaction time can be derived from the set instrument parameters. Therefore the absolute [[concentration]] of trace constituents <math>\lbrack R\rbrack</math> can be easily calculated without the need of [[calibration]] or gas standards. Furthermore it gets obvious that the overall sensitivity of a PTR-MS instrument is mainly dependent on the primary / reagent ion yield. Fig. 1 gives an overview of several published (in [[Academic journal|peer-reviewed journals]]) reagent ion yields during the last decades and the corresponding sensitivities.
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| == Technology ==
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| In commercial PTR-MS instruments water vapour is ionized in a hollow cathode discharge:
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| :<math>e^- + H_2O \longrightarrow H_2O^+ + 2e^-</math>
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| :<math>e^- + H_2O \longrightarrow H_2^+ + O + 2e^-</math>
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| :<math>e^- + H_2O \longrightarrow H^+ + OH + 2e^-</math>
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| :<math>e^- + H_2O \longrightarrow O^+ + H_2 + 2e^-</math>.
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| After the discharge a short drift tube is used to form very pure (>99.5%<ref name="Lindinger" />) H<sub>3</sub>O<sup>+</sup> via ion-molecule reactions:
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| :<math>H_2^+ + H_2O \rightarrow H_2O^+ + H_2</math>
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| :<math>H^+ + H_2O \rightarrow H_2O^+ + H</math>
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| :<math>O^+ + H_2O \rightarrow H_2O^+ + O</math>
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| :<math>H_2O^+ + H_2O \longrightarrow H_3O^+ + OH</math>.
| |
| Due to the high purity of the primary ions a mass filter between the ion source and the reaction drift tube is not necessary and the H<sub>3</sub>O<sup>+</sup> ions can be injected directly. The absence of this mass filter in turn greatly reduces losses of primary ions and leads eventually to an outstandingly low detection limit of the whole instrument.
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| In the reaction drift tube a [[vacuum pump]] is continuously drawing through air containing the VOCs one wants to analyze. At the end of the drift tube the protonated molecules are mass analyzed ([[Quadrupole mass analyzer]] or [[Time-of-flight mass spectrometry|Time-of-flight mass spectrometer]]) and detected.
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| === Advantages of PTR-MS ===
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| * ''Low fragmentation:'' Only a small amount of energy is transferred during the ionization process (compared to e.g. [[Electron ionization|electron impact ionization]]), therefore fragmentation is suppressed and the obtained [[Mass spectrum|mass spectra]] are easily interpretable.
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| * ''No sample preparation is necessary:'' VOC containing air and fluids headspaces can be analyzed directly.
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| * ''Real-time measurements:'' With a typical response time of 100 ms VOCs can be monitored on-line.
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| * ''Real-time quantification:'' Absolute concentrations are obtained directly without previous calibration measurements.
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| * ''Compact and robust setup:'' Due to the simple design and the low number of parts needed for a PTR-MS instrument, it can be built in into space saving and even mobile housings.
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| * ''Easy to operate:'' For the operation of a PTR-MS only [[electric power]] and a small amount of [[Purified water|distilled water]] are needed. Unlike other techniques no [[gas cylinder]]s are needed for buffer gas or calibration standards.
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| === Disadvantages of PTR-MS and countermeasures ===
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| * ''Not all molecules detectable:'' Because only molecules with a proton affinity higher than water can be detected by PTR-MS, proton transfer from H<sub>3</sub>O<sup>+</sup> is not suitable for all fields of application. Therefore in 2009 first PTR-MS instruments were presented, which are capable of switching between H<sub>3</sub>O<sup>+</sup> and [[Dioxygenyl|O<sub>2</sub><sup>+</sup>]] (and [[Nitrosonium|NO<sup>+</sup>]]) as reagent ions.<ref name="SRI">A. Jordan, S. Haidacher, G. Hanel, E. Hartungen, J. Herbig, L. Märk, R. Schottkowsky, H. Seehauser, P. Sulzer, T.D. Märk: An online ultra-high sensitivity proton-transfer-reaction mass-spectrometer combined with switchable reagent ion capability (PTR+SRI-MS), International Journal of Mass Spectrometry, 286, 32-38, ('''2009''').</ref> This enhances the number of detectable substances to important compounds like [[ethylene]], [[acetylene]], most [[halocarbon]]s, etc. In 2012 a PTR-MS instrument was introduced which extends the selectable reagent ions to [[Krypton|Kr<sup>+</sup>]] and [[Xenon|Xe<sup>+</sup>]];<ref>P. Sulzer, A. Edtbauer, E. Hartungen, S. Jürschik, A. Jordan, G. Hanel, S. Feil, S. Jaksch, L. Märk, T. D. Märk: From conventional Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) to universal trace gas analysis, International Journal of Mass Spectrometry (2012) http://dx.doi.org/10.1016/j.ijms.2012.05.003 .</ref> this should allow for the detection of nearly all possible substances (up to the ionization energy of krypton (14 eV<ref>[http://webbook.nist.gov/cgi/cbook.cgi?ID=C7439909&Units=SI&Mask=20#Ion-Energetics Krypton<!-- Bot generated title -->]</ref>)). Although the ionization method for these additional reagent ions is [[Charge-exchange ionization|charge-exchange]] rather than proton-transfer ionization the instruments can still be considered as "classic" PTR-MS instruments, i.e. no mass filter between the ion source and the drift tube and only some minor modifications on the ion source and vacuum design.
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| * ''Maximum measurable concentration limited:'' Equation (2) is based on the assumption that the decrease of primary ions is negligible, therefore the total concentration of VOCs in air must not exceed about 10 [[Parts-per notation|ppmv]]. Otherwise the instrument's response will not be linear anymore and the concentration calculation will be incorrect. This limitation can be overcome easily by diluting the sample with a well-defined amount of pure air.
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| == Applications ==
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| The most common applications for the PTR-MS technique are (including some relevant publications):<ref name="ptrmsHP" /><ref name="uibkHP" />
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| * [[Environmental science|Environmental research]]<ref>M. Müller, M. Graus, T. M. Ruuskanen, R. Schnitzhofer, I. Bamberger, L. Kaser, T. Titzmann, L. Hörtnagl, G. Wohlfahrt, T. Karl, A. Hansel: First eddy covariance flux measurements by PTR-TOF, Atmos. Meas. Tech., 3, 387–395, ('''2010''').</ref><ref>R. Beale, P. S. Liss, J. L. Dixon, P. D. Nightingale: Quantification of oxygenated volatile organic compounds in seawater by membrane inlet-proton transfer reaction/mass spectrometry. Anal. Chim. Acta ('''2011''').</ref>
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| * [[Incineration|Waste incineration]]
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| * [[Food science|Food and flavour science]]<ref>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''').</ref>
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| * [[Biology|Biological research]]<ref>M. Simpraga, H. Verbeeck, M. Demarcke, É. Joó, O. Pokorska, C. Amelynck, N. Schoon, J. Dewulf, H. Van Langenhove, B. Heinesch, M. Aubinet, Q. Laffineur, J.-F. Müller, K. Steppe: Clear link between drought stress, photosynthesis and biogenic volatile organic compounds in Fagus sylvatica L., Atmospheric Environment, 45, 5254-5259, ('''2011''').</ref>
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| * [[Cleanroom|Process monitoring]]
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| * [[Indoor air quality]]<ref>A. Wisthaler, P. Strom-Tejsen, L. Fang, T. J. Arnaud, A. Hansel, T. D. Märk, D. P. Wyon, PTR-MS Assessment of Photocatalytic and Sorption-Based Purification of Recirculated Cabin Air during Simulated 7-h Flights with High Passenger Density. Environ. Sci. Technol., 1/41, 229-234, ('''2007''').</ref><ref>B. Kolarik, P. Wargocki, A. Skorek-Osikowska, A. Wisthaler: The effect of a photocatalytic air purifier on indoor air quality quantified using different measuring methods, Building and Environment, 45, 1434–1440, ('''2010''').</ref><ref>K.H. Han, J.S. Zhang, H.N. Knudsen, P. Wargocki, H. Chen, P.K. Varshney, B. Guo: Development of a novel methodology for indoor emission source identification, Atmospheric Environment, 45, 3034-3045, ('''2011''').</ref>
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| * [[Medicine]] and [[biotechnology]]<ref>J. Herbig, M. Müller, S. Schallhart, T. Titzmann, M. Graus, A. Hansel, On-line breath analysis with PTR-TOF, J. Breath Res., 3, 027004, ('''2009''').</ref><ref>C. Brunner, W. Szymczak, V. Höllriegl, S. Mörtl, H. Oelmez, A. Bergner, R. M. Huber, C. Hoeschen, U. Oeh, Discrimination of cancerous and non-cancerous cell lines by headspace-analysis with PTR-MS, Anal. Bioanal. Chem., 397, 2315-2324, ('''2010''').</ref>
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| * [[Homeland Security]]<ref>S. Jürschik, P. Sulzer, F. Petersson, C. A. Mayhew, A. Jordan, B. Agarwal, S. Haidacher, H. Seehauser, K. Becker, T. D. Märk: Proton transfer reaction mass spectrometry for the sensitive and rapid real-time detection of solid high explosives in air and water, Anal Bioanal Chem 398, 2813–2820, ('''2010''').</ref><ref>F. Petersson, P. Sulzer, C.A. Mayhew, P. Watts, A. Jordan, L. Märk, T.D. Märk: Real-time trace detection and identification of chemical warfare agent simulants using recent advances in proton transfer reaction time-of-flight mass spectrometry, Rapid Commun. Mass Spectrom., 23, 3875–3880, ('''2009''').</ref>
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| Extensive reviews about PTR-MS and some of its applications were published in ''[[Mass Spectrometry Reviews]]'' by Joost de Gouw et al. (2007)<ref>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, 223-257, ('''2007''').</ref> and in ''[[Chemical Reviews]]'' by R.S. Blake et al. (2009).<ref>R. S. Blake, P. S. Monks, A. M. Ellis: Proton-Transfer Reaction Mass Spectrometry. Chem. Rev., 109/3, 861-896, ('''2009''').</ref> A special issue of the ''Journal of Breath Research'' dedicated to PTR-MS applications in medical research was published in 2009.<ref>Jens Herbig and Anton Amann (editors), Journal of Breath Research, Proton Transfer Reaction-Mass Spectrometry Applications in Medical Research; Volume 3, Number 2, June 2009.</ref>
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| == Examples ==
| |
| [[File:Ptr measurement of vanillin in breath.png|thumb|Fig. 2: PTR-MS measurement of vanillin dissemination in human breath. Isoprene is a product of human metabolism and acts as an indicator for breath cycles. (The measurement was performed utilizing a "N.A.S.E."<ref>[http://www.ionicon.com/products/accessories/nase.html Ionicon PTR-MS Accessories - N.A.S.E. Nosespace Air Sampling Extension<!-- Bot generated title -->]</ref> inlet system coupled to a "HS PTR-MS"<ref>[http://www.ionicon.com/products/ptr-ms/ptrqms/hs-ptr-qms_500.html Ionicon High-Sensitivity PTR-QMS 500 - 1 pptv real-time VOC detector<!-- Bot generated title -->]</ref> from IONICON Analytik, AUSTRIA.)]]
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| [[File:Ptr mass spectrum of lab air.png|thumb|Fig. 3: PTR mass spectrum of laboratory air obtained using a TOF based PTR instrument (PTR-TOF 8000;<ref>[http://www.ionicon.com/products/ptr-ms/ptrtofms/ptrtof8000.html High-Resolution PTR-TOF-MS IONICON PTR-TOF 8000 Ultimate Performance<!-- Bot generated title -->]</ref> IONICON Analytik, AUSTRIA).]]
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| === Food Science ===
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| Fig. 2 shows a typical PTR-MS measurement performed in food and flavor research. The test person swallows a sip of a [[vanillin]] flavored drink and breathes via his nose into a heated inlet device coupled to a PTR-MS instrument. Due to the high time resolution and sensitivity of the instrument used here, the development of vanillin in the person's breath can be monitored in real-time (please note that [[isoprene]] is shown in this figure because it is a product of human metabolism and therefore acts as an indicator for the breath cycles). The data can be used for food design, i.e. for adjusting the intensity and duration of vanillin flavor tasted by the consumer.
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| Another example for the application of PTR-MS in food science was published in 2008 by C. Lindinger et al.<ref>C. Lindinger, D. Labbe, P. Pollien, A. Rytz, M. A. Juillerat, C. Yeretzian, I. Blank, When Machine Tastes Coffee: Instrumental Approach To Predict the Sensory Profile of Espresso Coffee, ''Anal. Chem.'', 80/5, 1574-1581, ('''2008''').</ref> in ''[[Analytical Chemistry (journal)|Analytical Chemistry]]''. This publication found great response even in non-scientific media.<ref>[http://www.msnbc.msn.com/id/23359908/ Electronic nose knows quality coffee - Technology & science - Innovation - Frontiers | NBC News<!-- Bot generated title -->]</ref><ref>http://www.nytimes.com/2008/02/19/science/19objava.html?ex=1361077200&en=393e1220ba7a4cf1&ei=5124&partner=permalink&exprod=permalink</ref> Lindinger et al. developed a method to convert "dry" data from a PTR-MS instrument that measured headspace air from different [[coffee]] samples into expressions of [[Flavor|flavour]] (e.g. "woody", "winey", "flowery", etc.) and showed that the obtained flavor profiles matched nicely to the ones created by a panel of European coffee tasting experts.
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| === Air quality analysis ===
| |
| In Fig. 3 a mass spectrum of air inside a laboratory (obtained with a time-of-flight (TOF) based PTR-MS instrument), is shown. The [[amplitude|peaks]] on masses 19, 37 and 55 [[Mass-to-charge ratio|m/z]] (and their [[isotope]]s) represent the reagent ions (H<sub>3</sub>O<sup>+</sup>) and their clusters. On 30 and 32 m/z [[Nitric oxide|NO<sup>+</sup>]] and [[Oxygen|O<sub>2</sub><sup>+</sup>]], which are both impurities originating from the ion source, appear. All other peaks correspond to compounds present in typical laboratory air (e.g. high intensity of protonated [[acetone]] on 59 m/z). If one takes into account that virtually all peaks visible in Fig. 3 are in fact double, triple or multiple peaks ([[isobaric]] compounds) it becomes obivious that for PTR-MS instruments selectivity is at least as important as sensitivity, especially when complex samples / compositions are analyzed. Methods to handle this issue have been suggestested in literature as:
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| * ''High mass resolution'': When the PTR source is coupled to a [[Resolution (mass spectrometry)|high resolution]] mass spectrometer isobaric compounds can be distinguished and substances can be identified via their exact mass.<ref>A. Jordan, S. Haidacher, G. Hanel, E. Hartungen, L. Märk, H. Seehauser, R. Schottkowsky, P. Sulzer, T.D. Märk: A high resolution and high sensitivity time-of-flight proton-transfer-reaction mass spectrometer (PTR-TOF-MS), International Journal of Mass Spectrometry, 286, 122–128, ('''2009''').</ref>
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| * ''Switchable reagent ions'': Some PTR-MS instruments are despite of the lack of a mass filter between the ion source and the drift tube capable of switching the reagent ions (e.g. to NO<sup>+</sup> or O<sub>2</sub><sup>+</sup>). With the additional information obtained by using different reagent ions a much higher level of selectivity can be reached, e.g. some [[isomer]]ic molecules can be distinguished.<ref name="SRI" />
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| == References ==
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| {{reflist}}
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| [[Category:Mass spectrometry]]
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| [[Category:Measuring instruments]]
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To lower your likelihood of dеpreѕsion normallү, consume foods that have Vitamin supplement B6. Scientific research implies that B6 aѕsists control the body'ѕ amountѕ of serotonin. An imbalance of serotonin is a key reason behind depresѕive ɗisoгders. Some fоοd products with many ɗifferent ѕupplement B6 aгe chicken breasts, asparagus, and wheat bacteria. It will help during the wintertіme when prοblems are cool and quite often unhappy.
When you are in the fοօd store, allow your children to help you make alternatіves. When you allow them to opt for their vegatables and fruits, these are far more likely to consume them. Kids might also try out new meals this waу, particulaгly when they spot colorful fruit or veǥgіes.
Developing a habit of looking for new dishes can make іt easier to consume a wholesome dіet prоgram. The novelty and obstacle of making completely new dishеs encoսгages good behavior and prevents weight loss plans from being unappealing and repetitive. In this way, ɦaving a healthy diet plan could be more exciting insteaԁ of as a uninteresting chore.
If you're expecting, make certain you're getting sufficient steel in what you еat. An average grߋwnup woman ought to take in 18 mg of steel each day. Nonetheless, women that are pregnant ought to have 27 milligrams. The establishіng baby demands quite a lot of steel. If you do not get an extгa supplement, ʏοu could possibly produce anemia.
Should you ɑre unsuccessful one day, will not stress. Rather, commence ingesting wholesome the next day. Alloԝ it go likе a cheat time and commence new another day. Ѕimply being hard on on your own will not assist you to.
When you are prеgnant, you should exercise еxcellent diet, however, уou may still enjoy your preferred goodiеs from time to time. For one of the snack food items, get some fresh fruits, peanuts, or veggies instead. Allow on your own enjoy every so often and don't sense terrible regarding it.
An important nutrients idea wҺile being pregnant is making certain to add adequate calcium supplements every single day in what you eat. Babies will need calcium supplements for powerful bone and pearly whites, thus if they don't get sufficient in the new mothеr, they cоuld have a calcium sսpplements dеficiency.
It is important to take in meats. Tɦe proteins you obtain fгom beef can market your muscle progrеss. It doesn't issue if you eat beef, pork or fowl. Just make sure you get the nutrition that you requiгe. Aim to consume 15 oz . of various meats each day.
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