Delayed extraction


Delayed extraction
Delayed extraction with laser desorption ionization. Top: the laser fires at t=0 forming a fast "red" ion and slow "blue" ion of the same m/z, Middle: the red ion takes the lead since it has a greater velocity (and kinetic energy) but since it is farther from the acceleration plate at voltage +V, it gains less energy than the blue ion. Bottom: The blue ion has gained sufficient energy such that it arrives at the detector at the same time as the red ion.

Delayed extraction is a method used with a time-of-flight mass spectrometer 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.

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"[1]. With ions produced by laser desorption/ionization[2] or MALDI[3] [4] from a conductive surface of target plate, this is referred as "delayed extraction."

With delayed extraction, the mass resolution 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 have a higher velocity 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.

See also

References

  1. ^ Wiley, W. C.; McLaren, I. H. (1955), "Time-of-Flight Mass Spectrometer with Improved Resolution", Review of Scientific Instruments 26 (12): 1150, doi:10.1063/1.1715212 
  2. ^ V. 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.
  3. ^ Brown RS, Lennon JJ (July 1995), "Mass resolution improvement by incorporation of pulsed ion extraction in a matrix-assisted laser desorption/ionization linear time-of-flight mass spectrometer", Anal. Chem. 67 (13): 1998–2003, doi:10.1021/ac00109a015, PMID 8694246. 
  4. ^ Colby, Steven M.; King, Timothy B.; Reilly, James P.; Lubman, D. M. (1994), "Improving the resolution of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry by exploiting the correlation between ion position and velocity", Rapid Communications in Mass Spectrometry 8 (11): 865, doi:10.1002/rcm.1290081102 

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Oil shale extraction — is an industrial process in which kerogen mdash;a mixture of organic chemical compounds (including hydrocarbons) found in oil shale mdash;is converted into synthetic crude oil through pyrolysis. In pyrolysis, oil shale is heated in the absence of …   Wikipedia

  • Time-of-flight mass spectrometry — (TOFMS) is a method of mass spectrometry in which ions are accelerated by an electric field of known strength. [Stephens, W. E., [http://link.aps.org/abstract/PR/v69/p674/s2 A Pulsed Mass Spectrometer with Time Dispersion] Phys. Rev. , 1946, 69 …   Wikipedia

  • Guided bone regeneration — or GBR is a surgical procedure that uses barrier membranes to direct growth of new bone at sites having insufficient volumes or dimensions for function or prosthesis placement. GBR is similar to guided tissue regeneration (GTR) but is focused on… …   Wikipedia

  • Dental implant — Intervention A Straumann brand root form endosseous dental implant placed in the site of the maxillary left permanent first molar with bone graft used to elevate the sinus floor …   Wikipedia

  • Blowback (firearms) — Blowback is a system of operation for self loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the propellant charge.[1] Several types of blowback… …   Wikipedia

  • Blowback (arms) — Blowback is an operating system for autoloading firearms that utilizes energy created by combustion in the chamber and bore acting directly on the bolt face through the cartridge. Other operating systems are recoil operation, gas operation,… …   Wikipedia

  • Zinc — This article is about the metallic element. For other uses, see Zinc (disambiguation). copper ← zinc → gallium ↑ Zn ↓ Cd …   Wikipedia

  • china — /chuy neuh/, n. 1. a translucent ceramic material, biscuit fired at a high temperature, its glaze fired at a low temperature. 2. any porcelain ware. 3. plates, cups, saucers, etc., collectively. 4. figurines made of porcelain or ceramic material …   Universalium

  • China — /chuy neuh/, n. 1. People s Republic of, a country in E Asia. 1,221,591,778; 3,691,502 sq. mi. (9,560,990 sq. km). Cap.: Beijing. 2. Republic of. Also called Nationalist China. a republic consisting mainly of the island of Taiwan off the SE coast …   Universalium

  • environment — environmental, adj. environmentally, adv. /en vuy reuhn meuhnt, vuy euhrn /, n. 1. the aggregate of surrounding things, conditions, or influences; surroundings; milieu. 2. Ecol. the air, water, minerals, organisms, and all other external factors… …   Universalium