electron ionisation

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electron ionisation

The process of molecular ionisation initiated by the interaction of a gas-phase molecule with an energetic electron. The beam of electrons is emitted from a heated metal filament in the source; the electrons are then accelerated through a potential difference of 70 V. The collision between the molecule and the electron causes ejection of an electron from the molecule (M), and produces a radical molecular ion with the unpaired electron (M•).
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References in periodicals archive ?
As already stated, the vaporization surface of an electron ionization MS source is a key parameter for the detection and characterization of targeted and untargeted analytes: it is known that difficulties in the vaporization process arise when compounds characterized by high molecular weight and/or polarity have to be analyzed, thus requiring both the use of inert ion sources to reduce the interactions of the analytes with the stainless steel ion source and the use of high source temperatures to promote analyte vaporization.
Cappiello, "Electron ionization in LC-MS: recent developments and applications of the direct-EI LC-MS interface," Analytical and Bioanalytical Chemistry, vol.
A key feature of this variable-energy electron ionization technology, known as Select-eV, is the avoidance of sensitivity losses; absolute ion intensities at low energies have been found to be equal to or greater than 70 eV.
I have now completed systematic calculations of the electron ionization cross sections from all subshells that might be relevant for microanalysis.
In the electron ionization process, doubly charged argon is formed, leading to peaks at 20 (40[Ar.sup.++]) and 18 (36[Ar.sup.++]).
In the electron ionization (El) selected ion monitoring mode, it provides femtogram-level sensitivity.
Two principal methods are used to convert samples into ions: electron ionization (EI) and chemical ionization (CI).