Electron capture ionization

[1] 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.

[5] 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.

[3] With electrons of energy greater than 10 ev, negative ions can also be formed through ion-pair formation.

[5] Calibration of the mass spectrometer is important in electron capture ionization mode.

It is used to ensure that the mass scale used is correct and that the groups of ions are constant on a regular basis.

Argon and helium need to be combined with another gas, such as methane, in order to prevent immediate conversion into metastable ions.

Methane is the most common gas used because it can produce many positive ions when it collides with electrons.

These positive ions will then form low energy electrons used for ionization: An ECD is used in some gas chromatography systems.

Pesticide derivatives, nitrogen containing herbicides, and phosphorus-containing insecticides have also been detected in EC-MS.[3] Bile acids can detected in various body fluids by using GC-EC-MS. Oxidative damage can also be monitored in trace amounts by analyzing oxidized phenylalanine using GC-EC-MS.[4] EC-MS is a sensitive ionization method.

Increasing the pressure will help stabilize the anions and extend the lifetimes of the negative ions.