MALDI
Definition
Matrix-Assisted Laser Desorption / Ionisation. A soft method that uses a UV-absorbing matrix to ionise large biomolecules. Almost always paired with a TOF analyser.
- Full name
- Matrix-Assisted Laser Desorption/Ionisation
- Ionisation type
- Soft
- Typical analyte
- Large biomolecules
- Usual pairing
- TOF (time-of-flight) analyser
Common questions
Why is MALDI called a soft ionisation method?+
It ionises molecules with minimal fragmentation compared to hard ionisation methods like electron impact, which is essential for preserving large, fragile biomolecules such as proteins so their intact mass can be measured.
Why is MALDI almost always paired with a TOF analyser rather than another mass analyser?+
MALDI produces ions in short pulses from a laser strike, which suits TOF's pulsed measurement of flight time to the detector, giving the combination good sensitivity and mass range for large biomolecules.
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.
- 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.
- 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...
- 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.