ESI (Electrospray Ionisation)
Definition
Soft ionisation at atmospheric pressure for polar and thermally fragile analytes in solution. Standard source in LC-MS for drugs and biomolecules.
- Type
- Soft ionisation at atmospheric pressure
- Suited to
- Polar, thermally fragile analytes in solution
- Common pairing
- LC-MS
- Forensic use
- Drug and biomolecule analysis
Common questions
Why is ESI called a soft ionisation technique?+
It ionises molecules with minimal fragmentation compared with harsher techniques such as electron ionisation, so the resulting spectrum preserves the intact molecular ion, useful for confirming molecular mass rather than only fragment patterns.
Why is ESI paired with liquid chromatography rather than gas chromatography?+
ESI ionises analytes directly from a liquid stream at atmospheric pressure, which matches the liquid output of LC, whereas GC delivers analytes in the gas phase and pairs with ionisation sources designed for vapour-phase samples.
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...
- EI (Electron Ionisation)
- Hard ionisation at 70 eV. Produces extensive fragmentation, ideal for library search. Standard ion source in GC-MS.
- Fragmentation
- Breakdown of the molecular ion into smaller charged and neutral pieces. The fragmentation pattern is the chemical fingerprint that identifies the compound.
- 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...
- 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...
- 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.