Delayed extraction is a method used with a

time-of-flight mass spectrometer Time-of-flight mass spectrometry (TOFMS) is a method of mass spectrometry in which an ion's mass-to-charge ratio is determined by a time of flight measurement. Ions are accelerated by an electric field of known strength. This acceleration resu ...

in which the accelerating voltage is applied after some short time delay following pulsed laser desorption/ionization from a flat surface of target plate or, in other implementation, pulsed electron ionization or Resonance enhanced multiphoton ionization in some narrow space between two plates of the ion extraction system. The extraction delay can produce time-of-flight compensation for ion energy spread and improve

mass resolution In mass spectrometry, resolution is a measure of the ability to distinguish two peaks of slightly different mass-to-charge ratios ''ΔM'', in a mass spectrum. Resolution and resolving power There are two different definitions of resolution an ...

Implementation

Resolution can be improved in time-of-flight mass spectrometer with ions produced at high vacuum conditions (better than few microTorr) by allowing the initial packet ions to spread in space due to their translational energy before being accelerated into the flight tube. With ions produced by electron ionization or laser ionization of atoms or molecules from a rarefied gas, this is referred to as "time-lag focusing". With ions produced by laser desorption/ionizationV. S. Antonov, V. S. Letokhov, and A. N. Shibanov, (1980
Formation of molecular ions as a result of irradiation of the surface of molecular crystals
''Pis'ma Zh. Eksp. Teor. Fiz.'', 31, 471; ''JETP Lett.'', 31, 441. or

MALDI In mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) is an ionization technique that uses a laser energy absorbing matrix to create ions from large molecules with minimal fragmentation. It has been applied to the analysis of b ...

from a conductive surface of target plate, this is referred as "delayed extraction." With delayed extraction, the

is improved due to the correlation between velocity and position of the ions after those have been produced in the ion source. Ions produced with greater

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acc ...

have a higher

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

and during the delay time move closer to the extraction electrode before the accelerating voltage is applied across the target or pulsed electrode. The slower ions with less kinetic energy stay closer to a surface of the target electrode or pulsed electrode when the accelerating voltage is applied and therefore start being accelerated at a greater potential compared to the ions farther from the target electrode. With the proper delay time, the slower ions will receive enough extra potential energy to catch the faster ions after flying some distance from the pulsed acceleration system. Ions of the same mass-to-charge ratio will then drift through the flight tube to the detector in the same time.

References

{{Reflist Mass spectrometry

Implementation

See also

References