Matrix-assisted laser desorption/ionization pulsed

Brown, R. S. Lennon, J. J. Mass resolution improvement by incorporation of pulsed ion extraction in a matrix-assisted laser desorption/ionization linear time-of-flight mass spectrometer. Anal. Chem. 1995,67,1998-2003. 

R. S. Brown and J. J. Lennon. 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(1995) 1998-2003. 

Matrix assisted laser desorption ionization time-of-flight (MALDI-TOE) mass spectrometry was carried out with a PerSeptive Biosystems Voyager-DE-RP MALDl-TOF mass spectrometer. A 337-nm UV nitrogen laser producing 3-ns pulses was used in the reflectron mode. The samples were prepared by mixing 10 pi of a 0.1 M HAc solution of the sample with 20 pi of a solution of 3 mg/1 a-cyano-4-hydroxy cinnamic acid in wafer. One pi of that solution was loaded on the gold-sample plate. 

ToF mass spectrometers as dynamic instruments gained popularity with the introduction of matrix assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) as effective pulsed ion sources for the soft ionization of large biomolecules (up to 10s dalton) due to their high ion transmission.38 ToF mass spectrometers, quadrupole analyzers and/or magnetic sector fields can be combined in tandem mass spectrometers (MS/MS) for the analysis of organic compounds. 

Sequence of events in matrix-assisted laser desorption/ionization. (a) Dried mixture of analyte and matrix on sample probe inserted into backplate of ion source. (foZ) Enlarged view of laser pulse striking sample. (t>2) Matrix is ionized and vaporized by laser and transfers some charge to analyte. (b3) Vapor expands in a supersonic plume. 

Electrospray ionization and matrix-assisted desorption ionization were both introduced around the same time, in the late 1980s. In fact matrix-assisted laser desorption ionization (MALDI) was first mentioned in the literature in 1987 (Karas et al., 1987). In the years prior to that, there were limited reports of the application of laser desorption MS. Early developments in MALDI focused primarily on macromolecules, particularly peptides and proteins. Historically, MALDI ion sources have predominantly been coupled to time-of-flight (TOF) instruments. TOF requires precise timed ionization events, and since ions are generated in MALDI by a pulsed desorption, this combination is complementary. Mass spectra generated by MALDI can be relatively simple, containing predominantly singly charged ions. The importance of both ESI and MALDI are well proven in the analysis of biomolecules, and both techniques were awarded the Nobel Prize for chemistry in 2002 (Chapter 1). 

The critical aspect of this otherwise simple instrument is the need to produce the ions at an accurately known start time and position. These constraints generally limit TOF spectrometers to use pulsed ionization techniques, which include plasma and laser desorption (e.g., MALDI, matrix assisted laser desorption ionization). 

MALDI-MS refers to matrix-assisted laser desorption-ionization mass spectroscopy, It is also called MALFI-TOF, because the mass spectrometer is a time-of-flight version. In this technique, the polymer is mixed with a molar excess of a salt, for cationization, and deposited on a probe surface. A UV laser is pulsed... 

Mass spectrometry is one physical technique that does not (at least directly) involve electromagnetic radiation. However, some sample desorption and ionization processes do use high intensity pulses of laser light in techniques such as MALDI (Matrix-Assisted Laser Desorption Ionization) that have proved very useful in mass analysis of proteins and other biologic macromolecules. High resolution mass spectrometry derives from atomic/molecular beam studies in which the trajectories of ionized particles in a vacuum can be manipulated by static... 

Since its discovery, laser polymer processing has become an important field of applied and fundamental research. The research can be separated into two fields, the investigation of the ablation mechanism and its modeling and the application of laser ablation to produce novel materials. Laser ablation is used as an analytical tool in matrix-assisted laser desorption/ionization (MALDI) [12,13] and laser-induced breakdown spectroscopy (LIBS) [14] or as preparative tool for pulsed laser deposition (PLD) of synthetic polymers [15,16] and of inorganic films [17,18],... 

Laser Desorption and Matrix-Assisted Laser Desorption Ionization (MALDI). The use of a pulsed laser focused on a solid sample surface is an efficient method of ablating material from the surface and ionizing the material simultaneously. A variety of lasers have been used examples include IR lasers such as the CO2 laser (A = 10.6 jJLm) and UV lasers such as Nd YAG (A = 266 nm, 355 nm). (YAG stands for yttrium aluminum garnet). Selective ionization is possible by choosing the appropriate laser wavelength. The laser can be focused to a small spot, from submicron to several... 

Schematic representation of MALDI (matrix-assisted laser desorption ionization) in conjunction with mass spectromety. A protein salt is mixed into a matrix that is subjected to pulsed laser beams. Small volumes of matrix-bound proteins are aerosolized and stripped of matrix molecules under high vacuum.

Time-of-flight mass analyzers are most useful for pulsed ion sources, such as matrix-assisted laser desorption ionization (MALDI). The ions depart the source at the same time but arrive at the detector at different times depending on mass. These instruments have exceptionally high sensitivity and a high practical mass range. 

Schweer, J., Samecki, J., Mayer Posner, F., Mullen, K., Rader, H.J., and Spickermann, J., Pulsed-Laser Polymerization/Matrix-Assisted Laser Desorption/ionization Mass Spectrometry. An approach toward Free-Radical Propagation Rate Coefficients of Ultimate Accuracy, Macromolecules 29, 4536 (1996). 

Danis, P.O., Karr, D.E., Westmoreland, D.G., Piton, M.C., Christie, D.I., Clay, P.A., Kable, S.H., and Gilbert, R.G., Measurement of Propagation Rate Coefficients Using Pulsed-Laser Polymerization and Matrix-Assisted Laser Desorption/ Ionization Mass Spectrometry, Macromolecules, 26, 6684 (1993). 

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