Spectra in mass spectrometry

Ros stock, H.M. Krauss, M. Quasi-Equilibrium Theory of Mass Spectra, in Mass Spectrometry of Organic Ions, 1st ed. McLafferty, F.W., editor Academic... 

Beynon, J.H. Correlation of Molecular Structure and Mass Spectra, in Mass Spectrometry and its Applications to Organic Chemistry, 1st ed. Elsevier Amsterdam, 1960 pp. 352. 

Melton, C E. Negative ion Mass spectra, in Mass spectrometry of organic ions,... 

Electron ionization (earlier called electron impact) (see Chapter 2, Section 2.1.6) occupies a special position among ionization techniques. Historically it was the first method of ionization in mass spectrometry. Moreover it remains the most popular in mass spectrometry of organic compounds (not bioorganic). The main advantages of electron ionization are reliability and versatility. Besides that the existing computer libraries of mass spectra (Wiley/NIST, 2008) consist of electron ionization spectra. The fragmentation mles were also developed for the initial formation of a radical-cation as a result of electron ionization. 

Stereochemical aspects in mass spectrometry have aroused more and more interest. El mass spectra of stereoisomers are practically indistinguishable. However, the use of soft ionization methods (chemical ionization, field ionization, etc.) accompanied by tandem mass spectrometry allows important and reliable conclusions on the molecular structures to be drawn. 

Ortho-Effect. The ortho-effect is one of the most widely known structural phenomena in organic chemistry. It is widely used in organic chemistry for synthetic purposes. The mass spectra of the majority of ort/jo-substituted aromatic compounds possess significant differences in comparison with the spectra of their meta- and para-isomers. A classic example of the ortho-effect in mass spectrometry involves fragmentation of alkylsalicylates. The intense peaks of [M - ROH]+ ions dominate in the El spectra of these compounds. These peaks are absent in the spectra of their meta- and para-isomers. The reaction leading to these ions may be represented by Scheme 5.12. 

Figure 15.2. The SEC trace for a PC sample along with the MALDI spectra of sample PC2854 (upper spectrum) and of sample PC2780 (lower spectrum). (Reproduced from Puglisi, C. et al., 1999. Analysis of Poly(bisphenol A Carbonate) by Size Exclusion Chromatography/Matrix-Assisted Laser Desorption/lonization. I. End Group and Molar Mass Determination. Rapid Communications in Mass Spectrometry, 13 2260-2267. With permission of John Wiley Sons, Inc.)...

The volatility of the trimethylsilyl derivatives of the aldonolactones and related carbohydrates has made these derivatives suitable for use in mass spectrometry.161,162 Petersson and coworkers161,162 reported the mass spectra of a variety of trimethylsilyl derivatives of aldonolactones, including the spectrum of 54. 

Kurt Varmuza was bom in 1942 in Vienna, Austria. He studied chemistry at the Vienna University of Technology, Austria, where he wrote his doctoral thesis on mass spectrometry and his habilitation, which was devoted to the field of chemometrics. His research activities include applications of chemometric methods for spectra-structure relationships in mass spectrometry and infrared spectroscopy, for structure-property relationships, and in computer chemistry, archaeometry (especially with the Tyrolean Iceman), chemical engineering, botany, and cosmo chemistry (mission to a comet). Since 1992, he has been working as a professor at the Vienna University of Technology, currently at the Institute of Chemical Engineering. 

The quasi-equilibrium theory (QET) of mass spectra is a theoretical approach to describe the unimolecular decompositions of ions and hence their mass spectra. [12-14,14] QET has been developed as an adaptation of Rice-Ramsperger-Marcus-Kassel (RRKM) theory to fit the conditions of mass spectrometry and it represents a landmark in the theory of mass spectra. [11] In the mass spectrometer almost all processes occur under high vacuum conditions, i.e., in the highly diluted gas phase, and one has to become aware of the differences to chemical reactions in the condensed phase as they are usually carried out in the laboratory. [15,16] Consequently, bimolecular reactions are rare and the chemistry in a mass spectrometer is rather the chemistry of isolated ions in the gas phase. Isolated ions are not in thermal equilibrium with their surroundings as assumed by RRKM theory. Instead, to be isolated in the gas phase means for an ion that it may only internally redistribute energy and that it may only undergo unimolecular reactions such as isomerization or dissociation. This is why the theory of unimolecular reactions plays an important role in mass spectrometry. 

Fujii developed a method for detecting radical species in the gas phase with the use of lithium ion attachment to chemical species. Li ions have been chosen as reactant ions, because the affinity of the species is highest among all the alkah metal ions. The author also explored some of the unique properties of Li ion attachment in mass spectrometry. This technique provides mass spectra of quasi-molecular [R + Li]+ ions formed by lithium-ion attachment to the radical species under high pressure . ... 

Saturated Hydrocarbons Most of the work early in mass spectrometry was done on hydrocarbons of interest to the petroleum industry. Rules 1-3, (Section 2.7) apply quite generally rearrangement peaks, though common, are not usually intense (random rearrangements), and numerous reference spectra are available. 

Ionization Methods/Processes. The recent development of several new ionization methods in mass spectrometry has significantly improved the capability for the analysis of nonvolatile and thermally labile molecules [18-23]. Several of these methods (e.g., field desorption (FD), Californiun-252 plasma desorption (PD), fast heavy ion induced desorption (FHIID), laser-desorption (LD), SIMS, and fast atom bombardment (FAB) or liquid SIMS) desorb and ionize molecules directly from the solid state, thereby reducing the chance of thermal degradation. Although these methods employ fundamentally different excitation sources, similarities in their mass spectra, such as, the appearance of protonated, deprotonated, and/or cationized molecular ions, suggest a related ionization process. 

Bowie, J.H., Williams, D.H., Lawesson, S.O., Madsen, J.O., Nolde, C., and Schroll, G., Studies in mass spectrometry. XV. Mass spectra of sulphoxides and sulphones the formation of C-C and C-O bonds upon electron impact, Tetrahedron, 22, 3515, 1966. 

The addition of H2O2 to the mixtures containing 2-AF and peroxidase at pH 6.5 resulted in the rapid formation of a blue colour with an absorption maxima at 385 and 615 nm which reached a maximum in about 30 sec. The intensity of this colour was directly proportional to the enzyme and aminofluorene concentrations. One equivalent of H2O2 with respect to aminofluorene was required. The blue colour faded after this and became light brown after 5 mins. The blue colour disappeared upon extraction with ethyl acetate. The yellow extract was concentrated and applied to a TLC plate. The Rf of the various products is shown in Table III. Azofluorene was readily identified by its absorption spectra and mass spectrometry. The UV-visible absorption spectra had maxima in ethanol at 278 and 380 nm with shoulders at 362 and 396 nm. The mass spectrum showed a molecular ion at m/e 358.1463... 

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