TOF (Time-of-Flight)
Definition
Mass analyser that separates ions by their flight time down a field-free drift tube. Theoretically unlimited mass range, very high speed.
- Separation principle
- Ion flight time through a field-free drift tube
- Mass range
- Theoretically unlimited
- Speed
- Very high scan/acquisition speed
- Typical pairing
- GC-TOF or LC-TOF mass spectrometry
Common questions
How does flight time translate into a mass measurement?+
Ions of the same charge are accelerated by an identical electric field, so lighter ions travel faster down the drift tube and arrive at the detector sooner than heavier ones. The instrument converts each ion's precisely measured arrival time into a mass-to-charge ratio.
What advantage does TOF give over a quadrupole mass analyser in forensic work?+
TOF analysers can record the full mass spectrum for every ion pulse at high speed, which supports better chromatographic peak definition for fast separations and gives high mass accuracy useful for confirming compound identity in trace evidence.
Does TOF require a special ion source?+
TOF can be coupled to several ionisation methods, including electron ionisation for GC-TOF and electrospray for LC-TOF, so the choice of source depends on the sample type rather than being fixed by the TOF analyser itself.
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...
- 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...