Everything about Soft Laser Desorption totally explained
Soft laser desorption is
laser desorption of large molecules that results in
ionization without fragmentation. "Soft" in the context of
ion formation means forming ions without breaking
chemical bonds. "Hard" ionization is the formation of ions with the breaking of bonds and the formation of fragment ions.
Background
The term "soft laser desorption" hasn't been widely used by the
mass spectrometry community, which in most cases uses
matrix-assisted laser desorption/ionization (MALDI) to indicate soft laser desorption ionization that's aided by a separate matrix compound. The term soft laser desorption was used most notably by the
Nobel Foundation in public information released in conjunction with the 2002
Nobel Prize in Chemistry.
Koichi Tanaka was awarded 1/4 of the prize for his use of a mixture of
cobalt nanoparticles and
glycerol in what he called the “ultra fine metal plus liquid matrix method” of laser desorption ionization. With this approach, he was able to demonstrate the soft ionization of proteins. The MALDI technique was demonstrated (and the name coined) in 1985 by Michael Karas, Doris Bachmann, and Franz Hillenkamp, but ionization of proteins by MALDI wasn't reported until 1988, immediately after Tanaka's results were reported.
Some have argued that Karas and Hillenkamp were more deserving of the Nobel Prize than Tanaka because their crystalline matrix method is much more widely used than Tanaka's liquid matrix. Countering this argument is the fact that Tanaka was the first to use a 337 nm
nitrogen laser while Karas and Hillenkamp were using a 266 nm . The "modern" MALDI approach came into being several years after the first soft laser desorption of proteins was demonstrated.
Examples in mass spectrometry
The
matrix-assisted laser desorption/ionization approach typically uses a small organic acid solid matrix, although liquids have been used. The light source is a pulsed IR or UV laser. The
surface-enhanced laser desorption/ionization (SELDI) variand is similar to MALDI, but uses a biochemical affinity target. The technique known as surface-enhanced neat desorption (SEND) is a variant of MALDI with the matrix is covalently linked to the target surface.The surface-assisted laser desorption/ionization (SALDI) approach can be described as MALDI using a liquid plus particulate matrix. The desorption ionization on silicon (DIOS) approach is laser desorption/ionization of a sample deposited on a porous silicon surface. The technique known as laser induced acoustic desorption (LIAD ) is transmission geometry LDI with a metal film target.
Further Information
Get more info on 'Soft Laser Desorption'.
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