Matrix-assisted laser desorption electrospray ionization

Detection of radiolabeled proteins Mass spectrometry (electrospray ionization, matrix-assisted laser desorption, ionization) Gel electrophoresis (2D polyacrylamide gel electrophoresis)... 

The main sources used to analyze phenolic compounds are electron impact (El), chemical ionization (Cl), fast atom bombardment (FAB,) atmospheric pressure ionization (API) including atmospheric pressure chemical ionization (APCI) and atmospheric pressure photo-ionization (APPI), electrospray ionization (ESI), and in parallel to the advent of electrospray ionization, matrix-assisted laser desorption ionization (MALDI) [104—107, 112]. 

Tandem mass spectrometry (MS/MS) is a method for obtaining sequence and structural information by measurement of the mass-to-charge ratios of ionized molecules before and after dissociation reactions within a mass spectrometer which consists essentially of two mass spectrometers in tandem. In the first step, precursor ions are selected for further fragmentation by energy impact and interaction with a collision gas. The generated product ions can be analyzed by a second scan step. MS/MS measurements of peptides can be performed using electrospray or matrix-assisted laser desorption/ionization in combination with triple quadruple, ion trap, quadrupole-TOF (time-of-flight), TOF-TOF or ion cyclotron resonance MS. Tandem... 

Major methods for introducing proteins and other macromolecules into mass spectrometers are electrospray and matrix-assisted laser desorption/ionization (MALDI).18-27 Most often, MALDI is used with a time-of-flight mass spectrometer, which can measure mlz up to 106. Typically, 1 p,L of a 10 jxM solution of analyte is mixed with 1 p,L of a 1-100 mM solution of an ultraviolet-absorbing compound such as 2,5-dihydroxybenzoic acid (the matrix) directly on a probe that fits into the source of the spectrometer. Evaporation of the liquid leaves an intimate mixture of fine crystals of matrix plus analyte. 

Lehmann, W. D. (1996). Protease-catalyzed incorporation of 180 into peptide fragments and its application for protein sequencing by electrospray and matrix-assisted laser desorption/ ionization mass spectrometry. Electrophoresis 17, 945-953. 

Guittard, J., Tessier, M., Blais, J. C., Bolbach, G., Rozes, L., Mar6chal, E., and Tabet, J. C. Electrospray and matrix-assisted laser desorption/ionization mass spectrometry for the characterization of jxrlyesters. /. Mass Spectrom., 31,1409,1996. Deery M. J., Jennings, K. R., Jasieczek, C. B., Haddleton, D. M., Jackson, A. T., Yates, H. T., and Scrivens, J. H. A study of cation attachment to polystyrene by means of matrix-assisted laser desorption/ionization and electrospray ionization-mass sp>ectrometry. Rapid Commun. Mass Spectrom., 11, 57,1997. 

Barton, Z., Kemp, T. J., Buzy A., and Jermings, K. R. Mass spectral characterization of the thermal degradation of polyjpropylene oxide) by electrospray and matrix-assisted laser desorption ionization. Polymer, 36, 4927, 1995. 

Guittard, J., Tessier, M., Blais, J. C., Bolbach, G., Rozes, L., Marshal, E., and Tabet, J. C., Electrospray and Matrix-assisted Laser Desorption/Ionization Mass Spectrometry for the Characterization of Polyesters, /. Mass Spectrom., 31, 1409,1996. 

Electrospray and Matrix-Assisted Laser Desorption Ionization, Polymer, 36, 4927,1995. 

El and Cl methods can be used if the compound to be studied is sufficiently volatile and stable to be vaporized intact. However, only 20% of the organics found in surface water are volatile enough to be amenable to GC-EI-MS or GC-CI-MS. Today, there are a variety of other ionization techniques available electrospray ionization (ESI), atmospheric pressure chemical ionization, matrix-assisted laser desorption ionization, and fast atom bombardment. Each of these has its advantages and disadvantages. A simple guideline to the most likely optimum ionization technique for a given class of substance is given in Table 1. 

Shan, L, Murgasova, R Hercules, D.M., and Houalla, M. (2001) Electrospray and matrix-assisted laser desorption/ ionization mass spectral characterization of linear single nylon-6 oligomers./. 

Griffiths, W.J. Liu, S. Alvelius, G. SjovaU, J. Derivatisation for the characterisation of neutral oxoster-oids by electrospray and matrix-assisted laser desorption/ ionization tandem mass spectrometry The Girard P derivative. Rapid Commun. Mass Spectrom. 2003, 17 (9), 924-935. 

Lattova, E. Perreault, H. Labelling saccharides with phenylhydrazine for electrospray and matrix-assisted laser desorption-ionization mass spectrometry. J. Chromatogr. B 2003, 793, 167-179. 

A connnon feature of all mass spectrometers is the need to generate ions. Over the years a variety of ion sources have been developed. The physical chemistry and chemical physics communities have generally worked on gaseous and/or relatively volatile samples and thus have relied extensively on the two traditional ionization methods, electron ionization (El) and photoionization (PI). Other ionization sources, developed principally for analytical work, have recently started to be used in physical chemistry research. These include fast-atom bombardment (FAB), matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ES). 

FigureBl.7.2. Schematic representations of alternative ionization methods to El and PI (a) fast-atom bombardment in which a beam of keV atoms desorbs solute from a matrix (b) matrix-assisted laser desorption ionization and (c) electrospray ionization.

El = electron ionization Cl = chemical ionization ES = electrospray APCI = atmospheric-pressure chemical ionization MALDI = matrix-assisted laser desorption ionization PT = plasma torch (isotope ratios) TI = thermal (surface) ionization (isotope ratios). 

Most biochemical analyses by MS use either electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALD1), typically linked to a time-of-flight (TOF) mass analyzer. Both ESI and MALDl are "soft" ionization methods that produce charged molecules with little fragmentation, even with biological samples of very high molecular weight. 

Matrix-assisted laser desorption mass spectrometry (MALDI-MS) is, after electrospray ionization (ESI), the second most commonly used method for ionization of biomolecules in mass spectrometry. Samples are mixed with a UV-absorbing matrix substance and are air-dried on a metal target. Ionization and desorption of intact molecular ions are performed using a UV laser pulse. 

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. 

Matrix-assisted laser desorption ionization (MALDI) is not yet a technique that has been used extensively for LC-MS applications. It is included here because it often provides analytical information complementary to that obtained from LC-MS with electrospray ionization, as illustrated later in Chapter 5. 

The introduction and eventual commercialization of matrix-assisted laser desorption/ionization (MALDI) and electrospray (ESI) allowed biomarker status to be extended to proteins in 1996.15"17 With a few exceptions, ESI has been used in conjunction with extractions and high-pressure liquid chromatography (UPLC) interfaced with mass spectrometry. MALDI, on the other hand, has been widely adapted for rapid analysis of intact organisms, supported by bioinformatics.1819... 

It is therefore not surprising that the interest in PyMS as a typing tool diminished at the turn of the twenty-first century and hence why taxonomists have turned to MS-based methods that use soft ionization methods such as electrospray ionization (ESI-MS) and matrix-assisted laser desorption ionization (MALDI MS). These methods generate information-rich spectra of metabolites and proteins, and because the molecular ion is seen, the potential for biomarker discovery is being realized. The analyses of ESI-MS and MALDI-MS data will still need chemometric methods, and it is hoped that researchers in these areas can look back and learn from the many PyMS studies where machine learning was absolutely necessary to turn the complex pyrolysis MS data into knowledge of bacterial identities. 

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