Electron ionization-Mass spectrometry

Within mass spectrometry, electron ionization (El) typically results in the extensive fragmentation of the molecule under investigation. Therefore, the interpretation of the mass spectra (i.e., confirmation of molecular weight) can be difficult. A way to avoid fragmentation is via chemical ionization (Cl), which is done in our case using proton transfer reaction (PTR) ionization. Similar to Cl, molecules that are ionized using PTR techniques typically form a protonated molecular ion (M+H), in... 

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

Capillary Electrophoresis with Flame Photometric Detection Chemical Weapons Convention Extracted Ion Chromatogram Electron Impact Mass Spectrometry Electrospray Ionization Flow Injection Analysis Flame Photometric Detector Gas Chromatography/Fourier Transform Infrared Spectroscopy Gas Chromatography/Mass Spectrometry Gas chromatography International Union for Pure and... 

The electron ionization (El) source, formerly called electron impact, was devised by Dempster and improved by Bleakney [1] and Nier [2], It is widely used in organic mass spectrometry. This ionization technique works well for many gas-phase molecules but induces extensive fragmentation so that the molecular ions are not always observed. 

Both packed and capillary columns are used with the SFE-GC tandem. The detector is usually of the mass spectrometry, flame ionization or electron capture type. The most suitable interface for each application will be that allowing the extractant to be removed prior to the column — and hence to the detector. 

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. 

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. 

Veryovkin, I.V, Calaway, W.F., Moore, J.F, Pellin, M.J., Lewellen, J.W., Li, Y, Milton, S., King, B., Petravic, M. (2004) A new horizon in secondary neutral mass spectrometry post-ionization using a VUV free electron laser. Applied Surface Science, 231-232, 962-966. 

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.""... 

The species produced through ionization of an electron from a ir-orbital (such as from a C-H or a C-C bond of an alkane in mass spectrometry) cannot be represented at all by a connection table, yet the RAMSES notation can account for it as shown in Figure 2-59. 

Mass spectrometry is not based on absorption of electromagnetic radia tion but monitors what happens when a substance is ionized by collision with a high energy electron... 

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... 

For a limited range of substances, negative radical anions (M ) can be formed rather than positive ions (Equation 3.3). Negative radical anions can be produced in abundance by methods other than electron ionization. However, since most El mass spectrometry is concerned with positive ions, only they are discussed here. 

A further important use of El mass spectrometry lies in measuring isotope ratios, which can be used in estimating the ages of artifacts, rocks, or fossils. Electron ionization affects the isotopes of any one element equally, so that the true isotope ratio is not distorted by the ionization step. Further information on isotopes can be found in Chapter 46. 

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