Matrix-assisted laser desorption/ionization mechanisms

Two relatively new techniques, matrix assisted laser desorption ionization-lime of flight mass spectrometry (MALDI-TOF) and electrospray ionization (FS1), offer new possibilities for analysis of polymers with molecular weights in the tens of thousands. PS molecular weights as high as 1.5 million have been determined by MALDI-TOF. Recent reviews on the application of these techniques to synthetic polymers include those by Ilantoif54 and Nielen.555 The methods have been much used to provide evidence for initiation and termination mechanisms in various forms of living and controlled radical polymerization.550 Some examples of the application of MALDI-TOF and ESI in end group determination are provided in Table 3.12. The table is not intended to be a comprehensive survey. 

Kong Y, Zhu Y, Zhang J (2001) Ionization mechanism of oligonucleotides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Rapid Commun Mass Spectrom 15 57-64... 

Development of a wide range of Surface MALDI mass spectrometry methods12 opens new possibilities in MS investigations of bio-interfacial phenomena, summarized recently as biological surface science . Thus, matrix-assisted laser desorption ionization mass spectrometry, and its variants, hold promise to help clarify the mechanisms of bio-activity of silica-based nanocomposites. 

Knochenmuss, R., Dubois, F., Dale, M.J. and Zenobi, R. (1996) The matrix suppression effect and ionization mechanisms in matrix-assisted laser desorption/ionization. Rapid Conunun. Mass Spectram. 10, 871-877. 

A wide variety of desorption ionization methods is available [7] desorption chemical ionization (DCI), secondary-ion mass spectrometry (SIMS), fast-atom bombardment (FAB), liquid-SIMS, plasma desorption (PD), matrix-assisted laser desorption ionization (MALDI), and field desorption (FD). Two processes are important in the ionization mechanism, i.e., the formation of ions in the sample matrix prior to desorption, and rapid evaporation prior to ionization, which can be affected by very rapid heating or by sputtering by high-energy photons or particles. In addition, it is assumed that the energy deposited on the sample surface can cause (gas-phase) ionization reactions to occur near the interface of the solid or liquid and the vacuum (the so-called selvedge) or provide preformed ions in the condensed phase with sufficient kinetic energy to leave their environment. 

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],... 

The toluene-soluble fraction consists of a major product that has been identified as a CgQ-TEA monocycloadduct 7V-ethyl-rra/w-2, 5 -dimethyl-pyrrol-idino[3, 4 l,2][60]fullerene (14) by use of matrix-assisted laser desorption ionization mass spectroscopy and NMR methods [71]. It is interesting that the photochemical reaction actually results in the formation of a cycloadduct. This is unique to the fuilerene system because there have been no reports of cycloadducts in reactions involving nonfullerene acceptors [119-122], such as rra/is-stilbene. In the context of the classical photoinduced electron transfer-proton transfer mechanism [124], a two-step process for the formation of the cycloadduct has been proposed [71]. 

MALDI-TOF (matrix assisted laser desorption ionization time of flight) 51, 139 manufacture 244 manufacturers (CMOs) 129 market authorization application (MAA) 123 marketing authorization 205 mass spectrometry (MS) 104 mass spectroscopic analysis 175 master 67 master cell bank 139 matrigel 282 measles 63 mechanical 36 media components 104... 

The ionization source is the mechanical device that allows ionization to occur. Matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) are now the most common ionization sources for biomolecular MS, because both of them are soft ionization techniques that is, the sample ionization process generates few or no fragments even for large biomolecules, such as proteins and oligosaccharides, so that the intact molecular ions can be easily observed. 

Leukel, J., Burchard, W., Kruger, R. P, Much, H., and Schulz, G., Mechanism of the Anionic Copolymerization of Anhydride-cured Epoxies— Analyzed by Matrix-assisted Laser Desorption Ionization lime-of-flight Mass Spectrometry (MALDI-TOF-MS), Macromol. Rapid Commun., 17, 359,1996. 

Matrix-assisted laser desorption/ionization (MALDI) is one of the two soft ionization techniques besides electrospray ionization (ESI) which allow for the sensitive detection of large, nonvolatile and labile molecules by mass spectrometry. Over the past 27 years, MALDI has developed into an indispensable tool in analytical chemistry, and in analytical biochemistry in particular. In this chapter, the reader will be introduced to the technology as it stands now, and some of the underlying physical and chemical mechanisms as far as they have been investigated and clarified to date will be discussed. 

Berkenkamp, S., and Hillenkamp, F. (2001) Mechanisms of energy deposition in infrared matrix-assisted laser desorption/ionization mass spectrometry. Int. J. Mass Spectrom. Ion Processes, 207, 73-95. 

J. C. (2002) Post-source decay time-of-flight study of fragmentation mechanisms of protonated synthetic polymers under matrix-assisted laser desorption/ionization conditions. Rapid Commun. Mass Spectrom., 16, 596-704. 

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