Spectrometry electron impact

Photoionization-mass spectrometry Electron-impact lomzauon high-kinetic-energy ion beam... 

Mass Spectrometry. Electron impact (El) mass spectrometry was done at NRL on the effluent from a 6 ft. OV-101 packed GC column programmed from 70 to 210°C. Field ionization mass spectrometry (FIMS) was performed by SRI International on contract to NRL. In this latter analysis, the fuel sample was frozen on a solids inlet probe prior to insertion into the mass spectrometer. The spectra accumulated for each mass during a temperature program were normally totaled for data presentation (6). Molecules boiling below 140°C are lost or depleted with this technique but such compounds comprise a very small fraction of JP-5 or DFM. Since the ionization efficiency for hydrocarbon classes is currently under study, the FIMS data are utilized primarily in a qualitative sense. 

Confirmation by Mass Spectrometry. Extensive work was undertaken to confirm the Identity of all fluoroderlvatlves using mass spectrometry. Electron Impact fragmentation patterns confirmed the Identity of the mono-, dl- and trlfluoro derivatives of the octyl and octadecyl ligands and all of the species labeled In Figure 5. 

See also Dioxins. Gas Chromatography Column Technology Multidimensional Techniques High-Speed Techniques Instrumentation Detectors Mass Spectrometry. Lead. Mass Spectrometry Electron Impact and Chemical Ionization Ion Traps Selected Ion Monitoring. Mercury. Pesticides. Polychlorinated Biphenyls. Polycyclic Aromatic Hydrocarbons Determination. Tin. 

MASS SPECTROMETRY/Electron Impact and Chemical Ionization 359... 

See also Air Analysis Outdoor Air. Mass Spectrometry Electron Impact and Chemical Ionization Mass Separation Environmental Applications. Process Analysis Overview. Thermal Analysis Temperature-Modulated Techniques. 

Mass spectrometry (electron impact, field desorption, and chemical ionization ) in principal provides either a completely different, alternative method for peptide sequencing or a valuable supplement to the standard method. Applications have, however, been relatively few so far. Further studies on the mass spectral patterns obtained from model compounds have been reported. These should allow inter alia distinctions to be made between a- and y-glutamyl peptides and between leucyl and isoleucyl residues. Sequence studies on myoglobin from the bottle-nosed dolphin were facilitated by a computer comparison method. In this method, a peptide was either deuteroacetylated and deuteropermethylated or subjected to one step of the Edman degradation, followed by deuteroacetylation and deuteropermethylation. Comparison of the mass spectra of these derivatives aided the analysis.""... 

Section 13 22 Mass spectrometry exploits the information obtained when a molecule is ionized by electron impact and then dissociates to smaller fragments Pos itive ions are separated and detected according to their mass to charge (m/z) ratio By examining the fragments and by knowing how classes of molecules dissociate on electron impact one can deduce the structure of a compound Mass spectrometry is quite sensitive as little as 10 g of compound is sufficient for analysis... 

The behaviour under electron impact of IV- and C-trimethylsilylpyrazoles (mono-, di-and tri-substituted) has been studied by Birkofer et al. (740MS 8)347). Loss of a methyl radical followed by loss of HCN is the most common fragmentation feature of these compounds. When more than one trimethylsilyl group is present, a neutral fragment CaHgSi is expelled. Mass spectrometry of pyrazolium salts has been studied by Larsen etal. (8i OMS377, 830MS52). 

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). 

Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejected from a solid surface by energetic ion bombardment. The sputtered atoms are ionized for mass spectrometric analysis by a mechanism separate from the sputtering atomization. As such, SNMS is complementary to Secondary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms. The forte of SNMS analysis, compared to SIMS, is the accurate measurement of concentration depth profiles through chemically complex thin-film structures, including interfaces, with excellent depth resolution and to trace concentration levels. Genetically both SALI and GDMS are specific examples of SNMS. In this article we concentrate on post ionization only by electron impact. 

Electron-impact (El) Secondary Neutral Mass Spectrometry (SNMS)... 

Understanding how molecules fragment upon electron impact pennits a mass spectrum to be analyzed in sufficient detail to deduce the structure of an unknown compound. Thousands of compounds of known structure have been examined by mass spectrometry, and the fragmentation patterns that characterize different classes are well documented. As various groups are covered in subsequent chapters, aspects of their fragmentation behavior under conditions of electron impact will be described. 

Electron impact (Section 13.22) Method for producing positive ions in mass spectrometry whereby a molecule is bombarded by high-energy electrons. 

An on-line chromatography/atmospheric pressure chemical ionization tandem mass spectrometry (LC-APCI/MS/MS) methods was developed for rapid screen of pharmacokinetics of different drugs, including 5 (98RCM1216). The electron impact mass spectrum of 5 and ethyl 9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7Ff-pyrido[l,2,3- fe]-l,4-benzoxazine-6-carboxylate was reported (97MI28). Electron impact/Fourier transform... 

Electron impact/Fourier transform ion cyclotron resonance mass spectrometry was used to study the mass spectrum of 7 (96MI20). 

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