Electron-capture dissociation (ECD) is a method of fragmenting gas phase ions for tandem mass spectrometric analysis (structural elucidation). ECD involves the direct introduction of low energy electrons to trapped gas phase ions. It was developed by
Roman ZubarevRoman A. Zubarev is a professor of medical proteomics in the Department of Medical Biochemistry and Biophysics at the Karolinska Institutet. His research focuses on mass spectrometry...
and
Neil KelleherNeil L. Kelleher is a professor of chemistry at Northwestern University. His research focuses on mass spectrometry, primarily its application to proteomics. He is known mainly for top-down proteomics and the development of the fragmentation technique of electron-capture dissociation with Roman...
while in
Fred McLaffertyFred Warren McLafferty is an American chemist known for his work in mass spectrometry. He is best known for the McLafferty rearrangement reaction that was observed with mass spectrometry. WIth Roland Gohlke, he pioneered the technique of gas chromatography-mass spectrometry...
's lab at
Cornell UniversityCornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...
.
Principles
Electron-capture dissociation typically involves a multiply protonated molecule
M interacting with a free electron to form an odd-electron ion
.
Liberation of the
electric potential energyElectric potential energy, or electrostatic potential energy, is a potential energy that results from conservative Coulomb forces and is associated with the configuration of a particular set of point charges within a defined system...
results in fragmentation of the product ion.
ECD produces significantly different types of fragment ions (although primarily c- and z-type, b-ions have been identified in ECD) than other MS/MS fragmentation methods such as
electron-detachment dissociation (EDD)Electron-detachment dissociation is a method for fragmenting anionic species in mass spectrometry....
(primarily a and x type),
collision-induced dissociationIn Mass spectrometry, Collision-induced dissociation , referred to by some as collisionally activated dissociation , is a mechanism by which to fragment molecular ions in the gas phase. The molecular ions are usually accelerated by some electrical potential to high kinetic energy and then allowed...
(CID) (primarily b and y type) and
infrared multiphoton dissociationInfrared multiphoton dissociation is a technique used in mass spectrometry to fragment molecules in the gas phase usually for structural analysis of the original molecule. -How it works:...
. CID and IRMPD introduce internal vibrational energy in some way or another, causing loss of post-translational modifications during fragmentation. In ECD (and in EDD as well), fragments retain post-translational modifications such as phosphorylation and O-glycosylation. In ECD, unique fragments (and complementary to CID) are observed and the ability to fragment whole macromolecules effectively has been promising. The low fragmentation efficiencies and other experimental difficulties, which are being studied, have prevented widespread use. Although ECD is primarily used in
Fourier transform ion cyclotron resonanceFourier transform ion cyclotron resonance mass spectrometry, also known as Fourier transform mass spectrometry, is a type of mass analyzer for determining the mass-to-charge ratio of ions based on the cyclotron frequency of the ions in a fixed magnetic field...
mass spectrometry, investigators have indicated that it has been successfully used in an
ion trap mass spectrometerA quadrupole ion trap exists in both linear and 3D varieties and refers to an ion trap that uses constant DC and radio frequency oscillating AC electric fields to trap ions. It is commonly used as a component of a mass spectrometer...
.
ECD is a recently introduced MS/MS fragmentation technique and is still being investigated. The mechanism of ECD is still under debate but appears not to necessarily break the weakest bond and is therefore thought to be a fast process (
nonergodicIn physics and thermodynamics, the ergodic hypothesis says that, over long periods of time, the time spent by a particle in some region of the phase space of microstates with the same energy is proportional to the volume of this region, i.e., that all accessible microstates are equiprobable over a...
) where energy is not free to relax intramolecularly. Suggestions have been made that radical reactions initiated by the electron may be responsible for the action of ECD.
In a similar MS/MS fragmentation technique called electron-transfer dissociation the electrons are transferred by collision between the analyte cations and reagent anions.
See also
- Electron capture ionization
- electron–capture mass spectrometry
Electron-capture mass spectrometry 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...
- RRKM theory
The Rice–Ramsperger–Kassel–Marcus theory of chemical reactivity was developed by Rice and Ramsperger in 1927 and Kassel in 1928 . The RRK theory was generalized into the RRKM theory in 1952 by Marcus who took the transition state theory developed by Eyring in 1935 into account...