Time-of-Flight
Definition and meaning of Time-of-Flight in chemistry.
Time-of-flight (TOF) is a mass spectrometry technique that determines the mass-to-charge ratio (m/z) of ions by measuring the time required for them to travel through a fixed distance after acceleration by an electric field.
In more detail
Ions produced by ionization are accelerated through a known electric potential, gaining kinetic energy proportional to their charge and the voltage. They then drift through a field-free region at constant velocity, with lighter ions traveling faster and reaching the detector sooner than heavier ions of equal charge. The precise flight time is recorded and used to calculate mass from the fundamental relationship: flight time is proportional to the square root of mass-to-charge ratio. TOF mass spectrometry is widely used in analytical chemistry for its speed, high mass resolution, and ability to simultaneously measure a broad range of masses in a single acquisition.
Key facts
| Abbreviation | TOF or TOFMS (time-of-flight mass spectrometry) |
|---|---|
| Measurement basis | Flight time correlates with mass-to-charge ratio (m/z) |
| Detection timescale | Microseconds to tens of microseconds per measurement |
| Field | Analytical Chemistry |
When analyzing a protein digest by TOF-MS, peptide ions with m/z = 500 might reach the detector in 28 microseconds, while peptide ions with m/z = 1500 arrive in 49 microseconds; comparing these flight times to calibration standards allows identification of each peptide's molecular mass.
Frequently asked questions
How does TOF determine the mass of an ion?
Ions accelerated through the same voltage gain kinetic energy; lighter ions move faster through the drift region. By measuring flight time and comparing it to calibration standards, the exact mass-to-charge ratio is calculated from the fundamental physics of ion motion.
What are the main advantages of TOF over other mass spectrometry methods?
TOF analysis is rapid (entire mass range in microseconds), offers high mass accuracy and resolution, avoids radio-frequency scanning, and can detect ions across a wide mass range without changing instrument settings.