Glossary of Time of Flight Terms

Some text from Wikipedia.org

Time-of-flight mass spectrometry

TOFMS is a method of mass spectrometry where ions are accelerated by an electric field that has a known strength. This electric field acceleration results in an ion having the same kinetic energy as other ions that has the same charge. The velocity of the ion depends upon the mass-to-charge ratio. The time that it subsequently takes for the particle to travel to a detector at a known distance is then measured.

Delayed extraction

Delayed extraction refers to the operation mode of vacuum type ion sources when the onset of the electric field that is responsible for acceleration of the ions into the flight tube is delayed by a short time with respect to the ionization event. This differs from a constant extraction field where the ions are accelerated instantaneously as soon as they are formed.

Hadamard transform TOF

This type of  mass spectrometry is a TOF method that can be used with a continuous ion source. Whereas most TOF-MS analyzes only one packet of ions at a time, waiting for the ions to reach the detector before they can introduce another ion packet, HT-TOFMS analyzes several ion packets that are  in the flight tube at the same time.

Ion Gating

A Bradbury-Nielsen shutter is a type of ion gate that is used in TOF mass spectrometers and also in ion mobility spectrometers, as well as Hadamard transform TOF mass spectrometers. The Bradbury-Nielsen shutter is ideal for isolating ions that are over narrow mass range in tandem TOF MALDI mass spectrometers.

Orthogonal acceleration

Continuous ion sources (most commonly electrospray ionization or ESI) are generally interfaced to the TOF mass analyzer by “orthogonal extraction” in which ions introduced into the TOF mass analyzer are accelerated along an axis that is perpendicular to their initial direction of their motion.  Orthogonal acceleration combined with collisional ion cooling allows for separating the ion production in the ion source and hence mass analysis.

Reflection TOF

The kinetic energy distribution in the direction of the ion flight can be corrected by using a reflectron. The reflectron uses a constant electrostatic field to reflect the ion beam toward the detector. The more energetic ions will penetrate deeper into the reflectron, and hence take a slightly longer path to get to the detector.  Less energetic ions of the same charge-to-mass ratio will penetrate a shorter distance into the reflectron and, hence, take a shorter path to get to the detector.

Tandem TOF/TOF

Tandem TOF/TOF is a tandem mass spectrometry method where two time-of-flight mass spectrometers are used at the same time.  To record the full spectrum of precursor (parent) ions TOF/TOF operates in the MS mode. In this mode, the energy of the pulse laser is set slightly above the onset of MALDI for the specific matrix in use to ensure that the compromise between an ion yield for all of the parent ions and a reduced fragmentation of the same ions. When operating in this tandem (MS/MS) mode, the laser energy will be considerably above the MALDI threshold.