Mass spectrometry electron-impact

Electron impact mass spectrometry has been employed to study the fragmentation patterns of isoxazolylmethyl- and bis(isoxazolylmethyl)-isoxazoles and the results are in agreement with proposed pathways (79AC(R)8l). Electron impact studies of nitrostyryl isoxazole (6) show fragmentation in a variety of ways. The standard loss of NO2 from the molecular ion... 

Diphenylthiirene 1-oxide and several thiirene 1,1-dioxides show very weak molecular ions by electron impact mass spectrometry, but the molecular ions are much more abundant in chemical ionization mass spectrometry (75JHC21). The major fragmentation pathway is loss of sulfur monoxide or sulfur dioxide to give the alkynic ion. High resolution mass measurements identified minor fragment ions from 2,3-diphenylthiirene 1-oxide at mje 105 and 121 as PhCO" and PhCS, which are probably derived via rearrangement of the thiirene sulfoxide to monothiobenzil (Scheme 2). 

Description glycosidic cleavage to form an oxonium ion charge retained on nonreducing end positive-ion mode only often referred to as A -type cleavage, because of similarity to one of the cleavages seen in electron impact-mass spectrometry. 

Figure IQ Postulated structure for the major fragment ion of xenognosin B under electron impact mass spectrometry.

DRI Differential refractive index EI-MS, El MS Electron impact mass spectrometry... 

Purdon JG, Pagotto JG, Miller RK. 1989. Preparation, stability, and quantitative analysis by gas chromatography and gas chromatography-electron impact mass spectrometry of tert-butyldimethylsilyl derivatives of some alkylphosphonic and alkyl methylphosphonic acids. J Chromatogr 475 261-272. 

Lebedev et al. used electron impact mass spectrometry to induce the intramolecular cyclizations of dithiocarbamates of polyhalopyridines forming bis-l,3-dithiolo[4,5- 4, 5 -tf]pyridines, that are obtained by reaction in solution. Identical products were obtained under electron impact mass spectrometry (MS) conditions <1997JMP728>. 

Note. Abbreviations g.l.c., gas-liquid chromatography e.i.-m.s., electron-impact mass spectrometry c.i.-m.s., chemical-ionization mass spectrometry h.p.l.c., high-performance liquid chromatography h.p.a.e., high pH anion-exchange f.a.b.-m.s., fast-atom-bombardment mass spectrometry l.s.i.-m.s., liquid secondary-ion mass spectrometry n.O.e., nuclear Overhauser enhancement. Details of these methodologies are given in Ref. (3). 

Oswald EO, Albro PW, McKinney JD. 1974. Utilization of gas-liquid chromatography coupled with chemical ionization and electron impact mass spectrometry for the investigation of potentially hazardous environmental agents and their metabolites. J Chromatogr 98(2) 363-448. 

Ohashi, M. Nakayama, N. In-Beam Electron Impact Mass Spectrometry of Aliphatic Alkohols. Org. Mass Spectrom. 1978,13, 642-645. 

Rodriguez, J.G. Urrutia, A. Canoira, L. Electron Impact Mass Spectrometry of Indole Derivatives. Int. J. Mass Spectrom. Ion Proc. 1996, 752,97-110. 

All of the subsequent discussion of mass spectrometry is limited to positive-ion electron-impact mass spectrometry. 

Several recent reviews can provide the reader with an historical perspective and information about additional applications of chemical ionization mass spectrometry. (7-10) Under normal conditions, electron impact mass spectrometry is carried out by bombarding sample molecules with 70 eV electrons in a mass spectrometer ion source... 

Several investigators have utilized thermal techniques for the separation of sulfate species collected on filter media with subsequent analysis by electron impact mass spectrometry, wet chemical analysis or sulfur flame photometry. In most instances the separation between sulfuric acid and its ammonium salts was incomplete or problems were encountered in recovering the species of interest from filters heavily laden with particulate (29-34). 

Electron impact mass spectral analysis of sulfuric acid and sulfate salts (most notably ammonium sulfate) from filter samples has not been totally successful. Although the sensitivity of the technique was quite high (10 9 gms), both sulfuric acid and ammonium sulfate gave only SO3+. S02. SO+ fragments when analyzed by electron impact mass spectrometry. Since their spectra were very similar, accurate quantitation would require that only one species be introduced into the source at a... 

JHC297>. In a continuation of the above work, l,3,4-thiadiazolo[3,2-a][l,3,5]-triazines were also analyzed by electron impact mass spectrometry. A retro Diels-Alder process gave two fragments (Equation (1)) which in turn were further fragmented into smaller molecules. The mass spectral data for the 11 compounds analyzed has been tabulated in great detail <890MS(24)379>. 

Newton et al. developed a combination of DRIFTS, EXAFS and electron impact mass spectrometry (MS) which enables structure, function and... 

Some information has been obtained on the fragmentation patterns of 1,4-thiazine derivatives. A group of 2- and 3-substituted A-methylated benzothiazines with the general structure 2 (R = Me) lost a methyl radical in electron impact mass spectrometry at 70eV (Scheme 2) <1982J(P1)831>. 

Electron impact mass spectrometry is not effective to distinguish between the (Z) and (E) isomers of 4-benzylidene-2-phenyl-5(4//)-oxazolone and 4-(a-phenylethyl-idene)-2-phenyl-5(4//)-oxazolones because the spectra show only minor differences... 

Vreken P, Van Lint AEM, Bootsma AH, Overmars H, Wanders RJA, Van Gennip AH (1998) Rapid stable isotope dilution analysis of very-long-chain fatty acids, pristanic acid and phytanic acid using gas chromatography-electron impact mass spectrometry. J Chromatogr 713 281-287... 

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