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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Proton-transfer-reaction mass spectrometry ： ウィキペディア英語版 Proton-transfer-reaction mass spectrometry Proton-transfer-reaction mass spectrometry (PTR-MS) is an analytical chemistry technique that uses gas phase hydronium ions as ion source reagents. PTR-MS is used for online monitoring of volatile organic compounds (VOCs) in ambient air and was developed by scientists at the Institut für Ionenphysik at the Leopold-Franzens University in Innsbruck, Austria.〔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).〕 A PTR-MS instrument consists of an ion source that is directly connected to a drift tube (in contrast to 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 of about 100 ms and reach a detection limit in the single digit pptv region. Established fields of application are environmental research, food and flavour science, biological research, medicine, etc.〔(Ionicon PTR-MS Scientific Publications - PTR-MS Bibliography )〕〔(Publications – University of Innsbruck )〕 == Theory == With H3O+ as the primary ion the proton transfer process is (with $R$ being the trace component) :$H\_3O^+\; +\; R\; \backslash longrightarrow\; RH^+\; +\; H\_2O$ (1). Reaction (1) is only possible if energetically allowed, i.e. if the proton affinity of $R$ is higher than the proton affinity of H2O (691 kJ/mol〔R.S. Blake, P.S. Monks, A.M. Ellis, Proton-Transfer Reaction Mass Spectrometry, ''Chem. Rev.'', 109, 861-896 (2009)〕). As most components of ambient air possess a lower proton affinity than H2O (e.g. N2, O2, Ar, CO2, etc.) the H3O+ 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 H3O+ ions remains nearly unchanged, which leads to the equation〔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).〕 :$\backslash lbrack\; RH^+\backslash rbrack\; =\; \backslash lbrack\; H\_3O^+\backslash rbrack\_0\; \backslash left\; (1-e^\backslash right\; )\backslash approx\; \backslash lbrack\; H\_3O^+\backslash rbrack\; \_0\; \backslash lbrack\; R\backslash rbrack\; kt$ (2). In equation (2) $\backslash lbrack\; RH^+\backslash rbrack$ is the density of product ions, $\backslash lbrack\; H\_3O^+\backslash rbrack\_0$ is the density of primary ions in absence of reactant molecules in the buffer gas, $k$ is the reaction rate constant and $t$ 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〔Y. Ikezoe, S. Matsuoka and A. Viggiano, Gas Phase Ion-Molecule Reaction Rate Constants through 1986, ''Maruzen Company Ltd.'', Tokyo, (1987).〕 and the reaction time can be derived from the set instrument parameters. Therefore the absolute concentration of trace constituents $\backslash lbrack\; R\backslash rbrack$ 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 peer-reviewed journals) reagent ion yields during the last decades and the corresponding sensitivities. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Proton-transfer-reaction mass spectrometry」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.