Electron-capture mass spectrometry (EC-MS) is a type of mass spectrometry

Mass spectrometry

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...

 that uses electron capture ionization (ECI) to form negative ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s from chemical compounds with positive electron affinities

Electron affinity

The Electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion....

. The approach is particularly effective for electrophile

Electrophile

In general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...

s. In contrast to electron ionization

Electron ionization

Electron ionization is an ionization method in which energetic electrons interact with gas phase atoms or molecules to produce ions...

, EC-MS uses low energy electrons in a gas discharge. The technique can be used with gas chromatography-mass spectrometry

Gas chromatography-mass spectrometry

Gas chromatography–mass spectrometry is a method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC-MS include drug detection, fire investigation, environmental analysis, explosives investigation,...

.

Mechanism

The attachment of a low energy electron can give rise to two possible reactions for the compound, as shown below. Either the compound attaches an electron to form a radical

Radical (chemistry)

Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

 anion,
,

or the compound fragments, resulting in electron capture dissociation

Electron capture dissociation

Electron-capture dissociation is a method of fragmenting gas phase ions for tandem mass spectrometric analysis . ECD involves the direct introduction of low energy electrons to trapped gas phase ions...

 (ECD). ECD forms an anion fragment and a radical fragment
.

Fragmentation in ECI has been studied by tandem mass spectrometry

Tandem mass spectrometry

Tandem mass spectrometry, also known as MS/MS or MS2, involves multiple steps of mass spectrometry selection, with some form of fragmentation occurring in between the stages.-Tandem MS instruments:...

.