Electron Impact Mass Spectrometry EIMS

In this method the sample is vaporized in a micro-oven placed in the ion source or out of a Knudsen-cell. Many metals can be analyzed qualitatively and quantitatively by this technique as metal organic compounds (see Refs. ). The metal chelates have lower volatilities than the metals and in many cases the mass spectra reveal higher sensitivities for these compounds compared with the analysis using direct evaporation of the metal. The latter technique of direct metal analysis by EIMS is only applied if the ionization energies of the metals are too high for thermal ionization mass spectrometry . 

This mass spectrometric method for trace analysis is mainly used in multi-element analysis of surfaces and thin films. Also, microscopic distributions of elements in depth concentration profiles and in adsorption processes are determined - . A stable ion bombardment by a primary beam of a few kV is capable of ionizing atoms and molecules from the surface of a solid sample (about 100 A deep). 

Difficulties of SIMS are the complexity and large dynamic range of the ion beams produced. This may complicate the identification of the positive ion spectrum and cause sometimes an insufficient reproducibility of the results. Important advantages. 

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GC has been the main separation technique in the international interlaboratory comparison and proficiency tests a l4>. All participating laboratories used GC, either to determine the retention behavior of analyzed chemicals or as part of the hyphenated techniques. It has been agreed, on the basis of these tests, that the unambiguous identification of CWC-related chemicals has to be based on at least two different analysis techniques, preferably by two different spectrometric analysis techniques, when available, giving consistent results (15). The minimum acceptable data are the correct electron impact mass spectrometry (EIMS) spectrum together... 

Many ionization energies of neutral organometallic species, L MX, have been measured by electron impact mass spectrometry (EIMS) ... 

Extensive studies on the mass spectrometry of Amaryllidaceae alkaloids by electron impact were reported in the 1960s and 1970s 94,310,328,353,378-385). The fragmentation patterns in the electron impact mass spectrometry (EIMS) of various skeletal types are fairly well documented and have considerable diagnostic value. 

LAB or desulphonated LAS is prefactionated using argentation TLC, in which the TLC plate is coated with silver nitrate to modify the separation process, and analysed on a 30 mX 0.25 mm i.d. column of DB-5 (see comment in section 9.2.5) programmed from 35°C (10 min hold) to 290°C at 4°C per min with helium as carrier gas and GC/electron impact mass spectrometry (EIMS) detection [2]. 

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 ... 

Iron has four stable isotopes, Fe (5.8%), Fe (91.7%), Fe (2.2%), and Fe (0.3%). The radioactive iron isotope is Fe, which could easily be generated by nuclear reactors. The abundances and concentrations of stable iron isotopes could be determined by various isotope analytical methods. Several analytical approaches have been used in recent years for the determination of stable isotopes of minerals. These methods include NAA, inductively coupled plasma-mass spectrometry (ICP-MS), gas chromatography-mass spectrometry (GC-MS), electron impact mass spectrometry (EIMS), and magnetic sector, thermal... 

Abbreviations m/z is the mass-to-charge ratio, M is the molecular weight of the molecule itself, M+ is the molecular ion, HRMS is high-resolution mass spectrometry, FAB is fast atom bombardment, and EIMS is electron-impact mass spectrometry. 

EIMS electron impact mass spectrometry GPC gel permeation chromatography... 

We performed experimental research on the stability assessment of RVX and identification of its transformation products under the action of equimolar or excess amounts of water. The method for analysis was gas chromatography-electron impact mass spectrometry (GC-EIMS). In a dilute aqueous solution (lOmg/mL) in the presence of 5% phosphoric acid, the concentration of RVX after exposure for 20 days at room temperature without stirring was 2.7mg/mL, or 27% of the initial amount. Since among RVX hydrolysis products both volatile and nonvolatile compounds could be expected, we chose three schemes for sample preparation (i) evaporation to dryness followed by silylation (ii) organic solvent extraction and (iii) silylation of the extract obtained by procedure (ii). 

GC mass spectrometry analysis in electron impact mode (GC/EIMS) ... 

The correlation between the electron impact mass spectra of steroids and their structure has been a well-researched topic over the last twenty years. The success of mass spectrometry in this area owes much to the detailed analyses by Djerassi and co-workers. For unconjugated steroids, EIMS has been able to answer many structural questions. 

Two methods that have been used in tracer studies with are neutron activation analysis CNAA) and EIMS, mass spectrometry of a volatile chelate with electron impact ionization C15>19,20). Neither technique can match TIMS in accuracy or precision, but both may offer greater sample throughput. Until more precise techniques become more generally available, research utilizing stable metal isotopes will remain limited to the conditions imposed by the analytical facilities at hand. As will be shown below, research with stable magnesium isotopes to date, has had to be tailored to the limitations of available analytical techniques ... 

Mass Spectrometry with electron impact ionization (EIMS). Mass i ectrometers wit electron impact ionization are widely used in biomedical research, primarily for identification and quantitation of organic molecules. Adaptation of EIMS to isotope ratio measurements of minerals has, therefore, considerable appeal for investigators Interested in using stable mineral Isotopes as biological tracers. 

EIMS electron impact (ionizationi mass spectrometry... 

Figure 2 Traces obtained from simultaneous gas chromatography analysis of Maillard headspace, using both API and EIMS detectors. API, atmospheric pressure ionization El, electron impact MS, mass spectrometry.

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