Mass spectrometry, and ion—molecule

Knewstubb, P.F., Mass Spectrometry and Ion-Molecule Reactions, Cambridge University Press, London, 1969. Laeter, J.R. di. Applications of Inorganic Chemistry, Wiley, New York, 2001. 

Organophosphorus Chemistry series regularly lists new mass spectra in the Physical Methods chapter . With this in mind, an approach which considers fundamental aspects of organophosphorus ions (i.e. structure and reactivity) in the gas phase has been adopted. The gas-phase structure and reactivity of ions can be probed via several different techniques, including thermochemical measurements, kinetic energy release of metastable ions, collisional activation mass spectrometry, neutralization reionization mass spectrometry and ion-molecule reactions. An example is the molecule HCP (Table 1) its ionization potentiaP, proton affinity and the IR and rotational spectroscopy of the HCP ion " have all been determined in the gas phase. Another important tool for understanding the structure and reactivity of gas phase ions is ab initio molecular orbital theory. With advances in computational hardware and software, it is now possible to carry out high-level ab initio calculations on smaller systems. Indeed, the interplay between experiment and theory has fuelled many studies ... 

M. N. Eberlin, Triple-stage pentaquadrupole (QqQqQ) mass spectrometry and ion/molecule reactions. Mass Spectrom. Rev. 16, 113-144 (1997). 

Wang, Y.J., Han, H.Y., Shen, C.Y, Li, J.Q., Wang, H.M., Chu,Y.N. (2009) Control of solvent use in medical devices by proton transfer reaction mass spectrometry and ion molecule reaction mass spectrometry. Journal of Pharmaceutical and Biomedical Analysis, 50, 252-256. 

Eberlin MN. Triple-stage pentaquadmpole (QqQqQ) mass spectrometry and ion-molecule... 

P. F. Knewstubb, Mass Spectrometry and Ion-Molecule Reactions (Cambridge University Press, 1969). 

In the end, mass spectrometry and ion techniques will continue to be powerful tools for the investigation of the structure, bonding, energetics, and reactivity of unusual organic molecules. New sophisticated techniques will continue to be developed and applied to interesting problems in physical organic chemistry. These studies, along with the continued improvements in computational methods (Chapter 9), provide means to obtain very detailed and accurate descriptions of chemical reactions. 

Figure 2. The new species added to our chemical models of interstellar clouds. The species range in complexity from 10-64 carbon atoms and comprise the following groups of molecules linear carbon chains, monocyclic rings, tricyclic rings, and fullerenes. The synthetic pathways are also indicated. See ref. 83. Reproduced from the International Journal of Mass Spectrometry and Ion Processes, vol. 149/150, R.P.A. Bettens, Eric Herbst "The interstellar gas phase production of highly complex hydrocarbons construction of a model", pp 321-343 (1995) with kind permission from Elsevier Science-NL, Sara Burgerhartstraat 25,1055 KV, Amsterdam, The Netherlands.

Bushnell and co-workers [117] employed extensive molecular modelling to understand the nature of cis and trans isomerism in tetrahedral p-phenylene vinylene oligomers, and to aid the interpretation of time of flight mass spectrometry and ion mobility studies. Molecules such as T4R, shown in Figure 18, with four equivalent arms can be used to control the crystallinity in thin films. The authors reported the observation of a species in the mass spectrum resulting from the loss of an arm from the central carbon. This species will be referred to as P4R. 

Miller T. J. (1995). The chemistry of complex molecules in interstellar clouds. International Journal of Mass Spectrometry and Ion Processes 149/150 389. 

Spectrometry Spectroscopy4 is basically an experimental subject and is concerned with the adsorption, emission or scattering of electromagnetic radiation by atoms or molecules [15, p. 1]. A wide variety of applications of this concept have been applied in analyzing many substances. In the particular case of explosive molecules the most prominent are several forms of mass spectrometry and ion mobility spectrometry. Each has certain advantages and disadvantages. Each is discussed in detail in a later chapter. The former is most often used in fixed applications the latter, in both fixed and portable applications. 

Xu Y. and Herman J. A., Detection of nitrotoluene isomers by ion cyclotron resonance mass spectrometry using ion/molecule reactions with NO+ as reagent. Rapid. Commun. Mass. Spectrom., 6(7), 425-428, 1992. 

Kebarle P, Yamdagni R, Hiroaka JK and McMahon TB (1976) Ion molecule reactions at high pressure recent proton affinities, gas phase acidities and hydrocarbon clustering results. International Journal of Mass Spectrometry and Ion Physics 19 71-87. 

Dolnikowski, G.G., Kristo, M.J., Enke, C.G., and Watson, J.T. (1988) Ion-trapping technique for ion/molecule reaction studies in the center quadrupole of a triple quadrupole mass spectrometer. International Journal of Mass Spectrometry and Ion Processes, 82,1-15. 

This is the basic process in an inductively coupled plasma discharge (ICP). The excited ions can be examined by observing the emitted light or by mass spectrometry. Since the molecules have been broken down into their constituent atoms (as ions) including isotopes, these can be identified and quantified by mass spectrometry, as happens with isotope ratio measurements. 

These special features are explained by an interaction between the proton and one of the water molecules, which is not merely electrostatic but also covalent. This yields a new chemical species, the hydroxonium ion, HjO. The existence of such ions was demonstrated in the gas phase by mass spectrometry and in the solid phase by X-ray diffraction and nuclear magnetic resonance. The H -H20 bond has an energy of 712kJ/mol, which is almost two-thirds of the total proton hydration energy. 

If you are lucky, the ion with the highest mass to charge value will be the molecular ion. However, this is often not the case, as textbooks on mass spectrometry make clear. If it is possible to carry out high resolution mass spectrometry on the molecules in question, and the molecular ion is indeed observed, the exact mass can be used in combination with tables to obtain the molecular formula directly. Alternatively, you can use the internet (http //www.sisweb. com/cgi-bin/masslO.pl) to calculate and plot mass distributions for any molecular fragment you think may be present. 

Figure 2.9. Schematic of a matrix-assisted laser desorption/ionization (MALDI) event. The SEM micrograph depicts sinapinic acid-equine myoglobin crystal from a sample prepared according to the dried drop sample preparation method. In the desorption event neutral matrix molecules (M), positive matrix ions (M+), negative matrix ions (M-), neutral analyte molecules (N), positive analyte ions (+), and negative analyte ions (-) are created and/or transferred to the gas phase. Reprinted from A. Westman-Brinkmalm and G. Brinkmalm (2002). In Mass Spectrometry and Hyphenated Techniques in Neuropeptide Research, J. Silberring and R. Ekman (eds.) New York John Wiley Sons, 47-105. With permission of John Wiley Sons, Inc.

The production of ions from neutral compounds and the examination of how these ions subsequently fragment is fundamental to mass spectrometry. Neutral sample molecules can be ionized by a variety of processes. The most important of these for the production of positively charged species is the removal of an electron or the addition of one or more protons to give either molecular ions (M+ ) or protonated molecular species (M+nH)"+. This initial stage of ionization is often followed by fragmentation to produce ionized fragments, fragment ions . 

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