Electron capture ionization

Electron capture ionization is the ionization of a gas phase atom or molecule by attachment of an electron to create an ion of the form A. The reaction is

where the M over the arrow denotes that to conserve energy and momentum a third body is required (the molecularity of the reaction is three).

Electron capture can be used in conjunction with chemical ionization.

Electron-capture mass spectrometry (EC-MS) is a type of mass spectrometry that uses electron capture ionization to form negative ions from chemical compounds with positive electron affinities. The approach is particularly effective for electrophiles. In contrast to electron ionization, EC-MS uses low energy electrons in a gas discharge. EC-MS will cause less fragmentation of molecules compared to electron ionization.

Resonance electron capture is also known as nondissociative EC. The compound attaches an electron to form a radical anion. The energy of the electrons are about 0 eV. The electrons can be created in the Electron Ionization source with moderating gas such as H2, CH4, i-C4H10, NH3, N2, and Ar. After the ion captures the electron, the complex formed can stabilize during collisions and produce a stable anion that can be detected in a mass spectrometer.

In dissociative resonance capture, the compound fragments resulting in electron capture dissociation (ECD). ECD forms an anion fragment and a radical fragment. The energy of the electrons are from 0-15 eV, but the optimum energy can vary depending on the compound.

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