General information about what MALDI
2- Principle of working:
How does MALDI work
General information about techniques
4.2 Time of flight
4.3 Atmospheric pressure
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MALDI represents desorption ionization technique, induced by a laser beam and assisted by a matrix, while dynamic analyzer of resulting ions is based on ion time-of-flight (TOF). MALDI method allow direct ionization of solid samples to facilitate the analysis of large molecules with high molecular weight, such as proteins and polymers, which are thermally unstable and cannot sustain transition from solid to gas phase without decomposition (Stephen Shrader, Introductory Mass Spectrometry,2nd Edition, CRC Press).
In general, laser desorption mass spectrometry method developed in the 1960s, can be considered the beginning of soft ionization methods based on laser beams. The term "desorption ionization" denotes all ionization techniques in which ions are generated by desorption processes. It is based on the rapid supply of energy to the sample in the condensed phase (liquid or solid) with the subsequent formation and emission of stable ions in the gas phase. These are usually ionic species with an even number of electrons that are partially fragmented. As a result of the large number of studies devoted to the use of lasers as an energy source for ionizing molecules, the MALDI ionization technique emerged in the mid-1980s (Karas and Hillenkamp, 1988). And was quickly applied to the study of large molecules (Tanaka et al., 1988). Karas and Hillenkamp were the first to record spectra of molecular weight biomolecules above 10 kDa in the mixture of sample and the matrix (Karas and Hillenkamp, 1988). For the study of large biomolecules using the MALDI ionization technique Koichi Tanaka was awarded the 2002 Nobel Prize in Chemistry. In this chapter a brief overview of essential process taking place in MALDI will be given. This include most over used matrixes, ionization process description, lasers used as well as a description of most common analyzer (time-of-flight) used in ion detection.
2. The principle of MALDI
The matrix is a compound that exhibits strong absorption at the wavelength of the laser used, mixed with the analyte at a molar...