ELECTRON IMPACT MASS SPECTROSCOPY

Electron impact mass spectroscopy (70 eV, 200 C) of this compound gave a molecular ion at m/z 168.0389, and a chemical... 

Mulder, M. M., Van der Hage, E. R. E., and Boon, J. J., 1992, Analytical in source pyrolytic methylation electron impact mass spectroscopy of phenolic acids in biological matrices, Phytochem. Anal. 3 165-172. 

A series of angular-substituted octalins 84 and 85 were studied using electron-impact mass spectroscopy.86 It was found that the major fragmentation pathway of the derivatives 84 having a trans relationship between the silyl substituent and the angular substituent involved loss of the angular substituent... 

Methods for detecting cocaine and its metabolites in biological material have been reviewed.70 N.m.r. and i.r. spectroscopies, electron-impact mass spectroscopy,... 

During the early structural studies 60 MHz H-n.m.r. spectroscopy and electron impact mass spectroscopy were the most important physical tools used. Despite the great amount of information obtained by these physical methods, structural elucidation relied heavily on chemical transformations,... 

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 formation of thiopyrylium (2) as a rearrangement ion has been invoked in the electron impact mass spectra of 2- and 3-alkylthiophenes (59CCC1602 88IZV905). The tendency toward the formation of 2, which represents the most abundant species, grows as the side-chain increases in length. Cation 2 has been also detected in the reaction zone of a C Hg/ CS2/H2 flame, by flame ionization/mass spectroscopy (84AJC511). 

While the use of direct absorption methods has grown, indirect action spectroscopic methods continue to be widely and successfully used in the study of neutral molecular clusters. As mentioned earlier, there are two commonly used detection methods, mass spectrometers and bolometers. Because of the variety of mass-spectroscopic methods, there is an equally wide range of techniques used in neutral cluster spectroscopy. One of the oldest among these involves electron-impact mass spectrometry of a cw neutral beam combined with vibrational predissociation spectroscopy using a tunable cw or pulsed laser. The advent of continuously tunable infrared sources (such as color center lasers and LiNbOa optical parametric oscillators) allowed for detailed studies of size and composition variation in neutral clusters. However, fragmentation of the clusters within the ionizer of the mass spectrometer, severely limited the identification of particular clusters with specific masses. Isotopic methods were able to mitigate some of the limitations, but only in a few cases. 

Electron impact mass spectrometry provides the anticipated parent ion for oxathiocin (51) <91CPB1659> and thiazocinium derivatives (54 Ar = CsHj, P-CI-QH4) <76J0C818> (54 Ar = CeHj) also displays a significant fragment peak at M-93. IR spectroscopy of (51) shows, in addition to the carbonyl stretch at 1700 cm", bands at 1100 (C—O—C), 1060, and 965 cm" <91CPB1659>, while... 

Most of the compounds identified gave observable molecular ions in electron impact mass spectrometry. Chemical ionisation mass spectroscopy with isobutane was carried out to determine the relative molecular masses. In all instances, the quasi-molecular ion was M + 1 with a relative abundance of 10% no M + 57 was observed. Some compounds were identified on the basis of their mass spectra only because no reference compounds were obtainable. 

Removal of the Iti electron from NH(X S ) leads to the ionic ground state X removal of the 3a electron to the excited ionic states a A B A, and C Only a few experimental data for the first, third, and fourth ionization potentials Ej of gaseous NH are available. Resonance-enhanced multiphoton ionization (REMPI) of NH coupled with photoelectron spectroscopy (PES) yielded the most accurate results so far [1] and confirmed the values for the first E, obtained by electron-impact mass spectrometry (EIMS) [2] and by He I PES of NH [3]. Values for the second and third Ej to be observed in the He I PES of NH were predicted [3] from the optical emission spectra of NH [4]. Adiabatic and vertical Ej s (in eV) are compared in the following table ... 

Recent work has revealed that lipoxygenases from some plant tissues oxidize a-ketols of a-linolenic acid to hydroperoxides of a-ketols [3]. This paper deals with the formation of similar products by the other way by hydroperoxide dehydration of double dioxygenation products. Incubation of 9-hydroxy-16-hydroperoxy-10( ),12(Z),14( )-[l-l C]octadecatrienoic acid with enzyme preparation from com seeds led to the formation of three polar metabolites. After RP- and SP-HPLC purifications two of these polar metabolites were identified by UV spectroscopy and electron-impact mass spectrometry as a- and y-ketols of 9-hydroxy derivative of a-linolenic acid 9,16-dihydroxy-15-oxo-I0(, 12(Z)-octadecadienoic acid and 9,12-dihydroxy-15-oxo-I0(jE, 13( )-octadecadienoic acid, respectively. Stmcture of the most polar metabolite is discussed. 

In our recent work [4] formation of three polar metabolites from 9-hydroxy-I6-hydroperoxy-10( ),12(Z),14( )-octadecatrienoic acid in com enzyme preparation has been described. The stmcture of most prominent metabolite was identified by ultraviolet spectroscopy and electron-impact mass spectrometry as 15,16-a-ketol of 9-hydroxy derivative 9,16-dihydroxy-15-oxo-10(E), 12(Z)-octadecadienoic acid. 

This work shows the application of quantitative pyrolysis-gas chromatography coupled with infrared spectroscopy and electron impact mass spectrometry in the study of radiation-induced scission of bisphenol-A polycarbonate (PC). PC under vacuum was gamma-irradiated using a 60Co source in the dose range from 0.125 to 1.0 MGy. This was followed by flash pyrolysis under an inert atmosphere observed by GC-FTIR-MS. Pyrolysis of the irradiated PC gave different products depending on the dose. Yields of carbon dioxide and methane decreased with dose whereas those of phenol and 4-methylphenol increased. The yields of benzene and toluene were unaffected by irradiation. Analysis of the products in this study helped to infer two main pathways for the radiation-induced scission of PC that involve carbonate bond rupture or aliphatic-aromatic bond rupture. 30 refs. 

A more precise group of methods measure the beam equivalent pressure in molecular beams near the substrate or the atom fraction of interest in the gas phase. There are several ways of doing this including electron impact emission spectroscopy (EIES), conventional ionization gauges, mass spectrometers, glow-discharge optical spectroscopy, and other methods. We will briefly consider these four in turn. 

Nitrogen-containing fulvalenes have not been systematically studied by mass spectroscopy. Only isolated data for several examples of compounds have been reported. Most of the data consist of electron impact (El) mass spectra recorded for analytical purposes. Only a minor fraction dealt with the characterization of ion structures or focused on the effects of substituents, the ring size of fulvalenes, or the number and arrangement of nitrogen atoms and the fragmentation pathways. 

Mass spectroscopy is a useful technique for the characterization of dendrimers because it can be used to determine relative molar mass. Also, from the fragmentation pattern, the details of the monomer assembly in the branches can be confirmed. A variety of mass spectroscopic techniques have been used for this, including electron impact, fast atom bombardment and matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. 

A detailed description of sources used in atmospheric pressure ionization by electrospray or chemical ionization has been compiled.2 Atmospheric pressure has been used in a wide array of applications with electron impact, chemical ionization, pressure spray ionization (ionization when the electrode is below the threshold for corona discharge), electrospray ionization, and sonic spray ionization.3 Interferences potentially include overlap of ions of about the same mass-charge ratio, mobile-phase components, formation of adducts such as alkali metal ions, and suppression of ionization by substances more easily ionized than the analyte.4 A number of applications of mass spectroscopy are given in subsequent chapters. However, this section will serve as a brief synopsis, focusing on key techniques. 

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