EI (Electron Ionisation)

Definition

Hard ionisation at 70 eV. Produces extensive fragmentation, ideal for library search. Standard ion source in GC-MS.

Related terms

Base Peak: The most intense peak in a mass spectrum, normalised to 100 percent relative abundance. All other peaks in the spectrum are reported...
ESI (Electrospray Ionisation): Soft ionisation at atmospheric pressure for polar and thermally fragile analytes in solution. Standard source in LC-MS for drugs and biomolecules.
Fragmentation: Breakdown of the molecular ion into smaller charged and neutral pieces. The fragmentation pattern is the chemical fingerprint that identifies the compound.
MALDI: Matrix-Assisted Laser Desorption / Ionisation. A soft method that uses a UV-absorbing matrix to ionise large biomolecules. Almost always paired with a...
Molecular Ion (M+): The intact ionised molecule with no fragmentation, formed by removing a single electron from the parent. Its m/z gives the molecular weight...
M/z (Mass-to-Charge Ratio): The x-axis of every mass spectrum. Ions are separated by their mass divided by the number of charges they carry. For singly-charged...
Nitrogen Rule: An organic molecule with an odd-numbered molecular weight contains an odd number of nitrogen atoms. A staple trick for narrowing down a...
TOF (Time-of-Flight): Mass analyser that separates ions by their flight time down a field-free drift tube. Theoretically unlimited mass range, very high speed.

Mass Spectroscopy: Principles, Instrumentation and Forensic ApplicationsHard ionisation at 70 eV. Produces extensive fragmentation, ideal for library search. Standard ion source in GC-MS.