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Encyclopedia > MALDI

Matrix-Assisted Laser Desorption/Ionization (MALDI) is a soft ionization technique used in mass spectrometry, allowing, among others, to ionize biomolecules (biopolymers like proteins, peptides and sugarchains) which tend to be more fragile and quickly lose structure when ionized by more conventional ionization methods. It is most similar in character to electrospray ionization both in relative softness and ions produced. ... Mass spectrometry is a technique for separating ions by their mass-to-charge (m/z) ratios. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... A biopolymer is a polymer found in nature. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Peptides are the family of molecules formed from the linking, in a defined order, of various amino acids. ... Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions. ...


The ionization is triggered by a laser beam (normally a nitrogen-laser). A matrix is used to protect the biomolecule from being destroyed by direct laser beam. Laser (US Air Force) A LASER (Light Amplification by Stimulated Emission of Radiation) is an optical device which uses a quantum mechanical effect called stimulated emission (discovered by Einstein while researching the photoelectric effect) in order to generate a coherent beam of light from a lasing medium of controlled purity... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... Laser (US Air Force) A LASER (Light Amplification by Stimulated Emission of Radiation) is an optical device which uses a quantum mechanical effect called stimulated emission (discovered by Einstein while researching the photoelectric effect) in order to generate a coherent beam of light from a lasing medium of controlled purity... Laser (US Air Force) A LASER (Light Amplification by Stimulated Emission of Radiation) is an optical device which uses a quantum mechanical effect called stimulated emission (discovered by Einstein while researching the photoelectric effect) in order to generate a coherent beam of light from a lasing medium of controlled purity...

Contents


Matrix

The matrix consists of crystallized molecules, of which the three most commonly used are 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid), α-cyano-4-hydroxycinnamic acid (alpha-cyano or alpha-matrix) and 2,5-dihydroxybenzoic acid (DHB). A solution of one of these molecules is made, in a mixture of highly purified water and another organic compound (normally acetonitrile (ACN) or ethanol). Normally some trifluoroacetate (TFA) is also added. A good example of a matrix-solution would be 20 mg/mL sinapinic acid in ACN:water:TFA (50:50:0.1). Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... An acid (often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... Dissolving table salt in water In chemistry, a solution is a homogeneous mixture of one or more substances (the solutes) dissolved in another substance (the solvent). ... Water (from the Old English word wæter; c. ... A compound is an area of land that is surrounded by fences, walls, or barbed wire and is used for a particular purpose, especially an area containing buildings and where the entry and exit of people is controlled. ... Acetonitrile is an organic molecule, often used as a solvent, with the chemical formula of CH3CN. Also known as methyl cyanide, it is the simplest of the organic nitriles. ... Ethanol, also known as ethyl alcohol or grain alcohol, is a flammable, colorless chemical compound, one of the alcohols that is most often found in alcoholic beverages. ... Mg or mg or MG may stand for: machine gun Madagascar, ISO country code Malagasy language, in ISO 639 magnesium (Mg) MG (car), the car company milligram (mg) megagram (Mg) or Tonne MG stands for Minas Gerais, one of the states from Brazil Metal Gear or Metal Gear Solid This... mL (sometimes mℓ or ml in older usage) may stand for: millilitre(s) (also spelled mililiter), a thousandth of a litre in the metric system ML may stand for megalitre(s) (also spelled megaliter), a million litres in the metric system or any the following computing-related terms: in artificial...


The matrix-solution is then mixed with the analyte molecule (e.g. protein-sample) which you wish to investigate. The organic compound ACN allows for the hydrophobic proteins in the sample to dissolve into the solution, while the water allows for water-soluble (hydrophilic) proteins to do the same. This solution is spotted onto a MALDI plate (usually a metal plate designed for this purpose). The solvents vaporize, leaving only the recrystallized matrix, but now with proteins spread throughout the crystals. The matrix and the analyte are said to be co-crystalized in a MALDI spot. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ...


Laser

The laser is fired at the crystals in the MALDI spot. The spot absorbs the laser energy and it is thought that primarily the matrix is ionized by this event. The matrix is then thought to transfer part of their charge to the analyte (e.g. a protein), thus ionizing them while still protecting them from the disruptive energy of the laser. Ions observed after this process are quasimolecular ions that are ionized by the addition of a proton to [M+H], or other cation such as sodium ion [M+Na], or the removal of a proton [M-H] for example. MALDI generally produces singly-charged ions, but doubly-charged ions such as [M+2H] have been observed as well. Note that these are all even-electron species. Electrons themselves (alone) have neither been added or removed, as is the case in some other ionizations. Laser (US Air Force) A LASER (Light Amplification by Stimulated Emission of Radiation) is an optical device which uses a quantum mechanical effect called stimulated emission (discovered by Einstein while researching the photoelectric effect) in order to generate a coherent beam of light from a lasing medium of controlled purity... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ...


Mass spectrometer

The proteins are then ready to be extracted into a mass spectrometer. A common type of a MALDI spectrometer is the MALDI-TOF, with TOF standing for Time-of-flight. Usually the ionized proteins in MALDI are not measured by deflection, but by the amount of time it takes for them to traverse a certain distance. The ionized particles are accelerated using a voltage which corresponds to a certain kinetic energy (and can even be subjected to a velocity discriminator). Then they traverse a tube and the amount of time from acceleration to detection is recorded. This can then be used to calculate velocity, and thus mass. Mass spectrometry is a technique for separating ions by their mass-to-charge (m/z) ratios. ... The Time of flight method of measuring particle mass is done as follows. ...


Precision can be enhanced by increasing the length of the tube. Since MALDI machines are typically tabletop, there is a practical restriction on the precision afforded by this technique. Some MALDI machines have a "reflectron" which acts as a "mass mirror", deflecting particles with an electric charge at the end of the tube, thus nearly doubling the traveling distance and increasing precision.


Koichi Tanaka received 1/4 of the 2002 Nobel Prize in Chemistry for Macromolecule Ionization by Laser Irradiation, however, Matrix-Assisted Laser Desorption/Ionization (MALDI) was created by M. Karas and F. Hillenkamp. Koichi Tanaka (田中 耕一, born August 3, 1959) is a Japanese scientist who won the Nobel Prize in Chemistry in 2002 for developing a novel method for mass spectrometric analyses of biological macromolecules. ... 2002 is a common year starting on Tuesday of the Gregorian calendar. ... List of Nobel Prize laureates in Chemistry from 1901 to the present day. ...


See also

Peptide mass fingerprinting // Abstract Peptide mass fingerpring (PMF) is an analytical technique for protein identification that was developed by John Yates and colleagues (3). ...


Mass spectrometer makers

  • Applied Biosystems
  • Bruker Daltonics
  • Micromass
  • Shimadzu

Reference

  • Karas M, Hillenkamp F Laser desorption ionization of proteins with molecular masses exceeding 10,000 daltons.Anal Chem. 1988 Oct 15;60(20):2299-301.

  Results from FactBites:
 
Characterizing Synthetic Polymers by MALDI MS (3435 words)
MALDI is a "soft" ionization process that produces (quasi)molecular ions from large nonvolatile molecules, such as proteins, oligonucleotides, polysaccharides, and synthetic polymers, with minimum fragmentation.
MALDI generates high-mass ions by irradiating a solid mixture of an analyte dissolved in a suitable matrix compound with a pulsed laser beam.
The concept involves combining MALDI with chromatography: The intensity of the polymer present (the relative abundance of the polymer distribution) is determined by the refractive index response of GPC, and the mass of the eluant is then measured by a mass spectrometer.
Matrix-assisted laser desorption/ionization - Wikipedia, the free encyclopedia (1284 words)
Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique used in mass spectrometry, allowing, among other things, the ionization of biomolecules (biopolymers such as proteins, peptides and sugars) which tend to be more fragile and quickly lose structure when ionized by more conventional ionization methods.
The term matrix-assisted laser desorption ionization (MALDI) was coined in 1985 by Franz Hillenkamp, Michael Karas and their colleagues (Karas et al, 1985).
In proteomics, MALDI is used for the identification of proteins isolated through gel electrophoresis: SDS-PAGE and two-dimensional gel electrophoresis.
  More results at FactBites »

 
 

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