Proton transfer reaction mass

It is possible to measure equilibrium constants and heats of reaction in the gas phase by using mass spectrometers of special configuration. With proton-transfer reactions, for example, the equilibrium constant can be determined by measuring the ratio of two reactant species competing for protons. Table 4.13 compares of phenol ionizations. 

However, a closer inspection of the experimental data reveals several differences. For ion-transfer reactions the transfer coefficient a can take on any value between zero and one, and varies with temperature in many cases. For outer-sphere electron-transfer reactions the transfer coefficient is always close to 1/2, and is independent of temperature. The behavior of electron-transfer reactions could be explained by the theory presented in Chapter 6, but this theory - at least in the form we have presented it - does not apply to ion transfer. It can, in fact, be extended into a model that encompasses both types of reactions [7], though not proton-transfer reactions, which are special because of the strong interaction of the proton with water and because of its small mass. 

Because of their dependence on mass, KIEs have been used in two ways to detect tunnelling. One is that primary deuterium KIEs are larger than predicted on the basis of zero-point energy alone when tunnelling makes a significant contribution to the KIE. For example, primary deuterium KIEs larger than 25 have been reported (Lewis and Funderburk, 1967 Wilson et al., 1973) for proton transfer reactions where tunnelling is important. 

Sometimes, FI mass spectra show signals due to reactions of the analyte with the emitter surface or between molecules adsorbed to that surface. In case of acetone for example, it was demonstrated that [M+H]" quasimolecular ions are produced mainly by a field-induced proton-transfer reaction in the physically adsorbed layer. [59] The mechanism of this field-induced reaction depends on the existence of tautomeric structures of the neutral molecule. Besides the [M+H] quasimolecular ions, [M-H] radicals are formed ... 

Gimon, M.E. Preston, L.M. Solouki, T. White, M.A. Russel, D.H. Are Proton Transfer Reactions of Excited States Involved in UV Laser Desorption Ionization Org. Mass Spectrom. 1992, 27, 827-830. 

Karl, T., Yeretzian, C., Jordan, A., and Lindinger, W. Dynamic measurements of partition coefficients using proton-transfer-reaction mass spectrometry (PTR-MS), Int. J. Mass Spectrom., 223-224 383-395, 2003. 

Steeghs M, Bais HP, de Gouw J, Goldan P, Kuster W, Northway M, Fall R, Vivanco JM (2004) Proton-transfer-reaction mass spectrometry as a new tool for real time analysis of root-secreted volatile organic compounds in arabidopsis. Plant Physiol 135 47-58... 

Kushch 1, Arendacka B, Stoic S et al (2008) Breath isoprene - aspects of normal physiology related to age, gender and cholesterol profile as determined in a proton transfer reaction mass spectrometry study. Clin Chem Lab Med 46(7) 1011-1018... 

Fig. 15.14 Analytical techniques for time-resolved headspace analysis. An electronic nose can be used as a low-cost process-monitoring device, where chemical information is not mandatory. Electron impact ionisation mass spectrometry (EI-MS) adds sensitivity, speed and some chemical information. Yet, owing to the hard ionisation mode, most chemical information is lost. Proton-transfer-reaction MS (PTR-MS) is a sensitive one-dimensional method, which provides characteristic headspace profiles (detailed fingerprints) and chemical information. Finally, resonance-enhanced multiphoton ionisation (REMPI) TOFMS combines selective ionisation and mass separation and hence represents a two-dimensional method. (Adapted from [190])...

Coupling of Proton-Transfer-Reaction Mass Spectrometry with Gas Chromatography-Mass Spectrometry... 

Lindinger, W., Fall, R., Karl, T.G. (2001) Environmental, food and medical applications of proton-transfer-reaction mass spectrometry (PTR-MS). Adv. Gas Phase Ion Chem. 4 1-48. 

Taylor, A.J., Sivasundaram, L.R., Linforth, R.S.T., Surawang, S. (2003) Time-resolved head-space analysis by proton-transfer-reaction mass-spectrometry. In Deibler, K.D., Delwiche, J. (eds) Handbook of Flavor Characterization. Sensory Analysis, Chemistry and Physiology. Dekker, New York, pp 411-422. 

A proton transfer reaction-mass spectrometer (PTR-MS) system has been developed which allows on-line measurement of VOCs with concentrations as low as a few pptv (parts per trillion by volume) (Hansel et al., 1998). The acute measurement sensitivity to VOCs and real-time characteristics make it a very powerful tool in both indoor and outdoor environmental research. 

The resultant ions (both primary and produced) are mass-selected using a quadruple mass analyzer and measured as count rates by an electron multiplier detector. Count rates of the MH+ species are subsequently converted to ionic densities and then to mixing ratios of constituent M after consideration of instrumental transmission coefficients, temperature, and DT pressure. Instrumental accuracy, which is largely determined by the uncertainties associated with the reported proton transfer reaction rate coefficients (k), is estimated to be better than 30% (Hayward et al, 2002 Lindinger, Hansel and Jordan, 1998). 

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