Electrospray ionization MALDI mass

Figure 14.1 Schematic view of a mass spectrometer. Its basic parts are ion source, mass analyzer, and detector. Selected principles realized in modern mass spectrometers are assigned El—electron impact. Cl—chemical ionization, FAB—fast atom bombardment, ESI—electrospray ionization, MALDI—matrix-assisted laser desorption/ionization. Different combinations of ion formation with mass separation can be realized.

Mass spectrometry has played a role in biochemistry since the early 1940s when it was introduced for use in following isotopic labels during metabolism.199-20 However, it was not until the 1990s that suitable commercial instruments were developed to permit mass spectrometry using two new methods of ionization. The techniques are called matrix-assisted laser desorption / ionization time-of-flight (MALDI-TOF) and electrospray ionization (ESI) mass spectrometry. 

Guaratini T, Vessecchi RL, Lavarda FC, Maia Campos PM, Naal Z, Gates PJ, Lopes NP. New chemical evidence for the ability to generate radical molecular ions of polyenes from ESI and HR-MALDI mass spectrometry. Analyst 2004,129 1223-1226 Guaratini T, Vessecchi R, Pinto E, Colepicolo P, Lopes NP. Balance of xanthophylls molecular and protonated molecular ions in electrospray ionization. J Mass Spectrom 2005 40 963-968. 

The unimolecular fragmentation of calixarene-derived ions will not be treated here, especially as studies on this topic are much restricted due to the fact that classical El and Cl techniques cannot be applied to these mvolatile and often quite polar polyphenols. Rather, mass spectrometric analysis is limited to the detection of positively or negatively charged quasi-molecular ions, such as [M + H]+ and [M — H], or molecular adduct ions, such as [M + NR4]+ and [M - - metal]+. In general, these ions can be readily generated by using matrix-assisted laser desorption (MALDI) and/or electrospray ionization (ESI) mass spectrometry. 

Selva and coworkers - reported on their experiences to apply various mass spectrometric techniques to the analysis of -carotene and carotenoids and their adducts formed in aqueous solution. El mass spectrometry and field desorption (FD) mass spectrometry were applied to aqueous mixtures of -carotene and /J-cyclodextrin, and the polyene was found to be detectable . Tandem mass spectrometry can be applied to identify fi-carotenone as a minor component in complex carotenoid mixtures. EI/MIKE spectrometry of the molecular ion m/z 600) was used in this case . A previous study was focused on the characterization of. vecw-carotcnoids using EI/MIKE and CID spectrometiy . The more recent ionization methods, viz. MALDI and its variant working without a matrix, laser desorption/ionization (EDI), as well as electrospray ionization (ESI) mass spectrometry, have also been applied to this topic. MALDI and LDI mass spectrometry were used to analyse mixtures of -carotene and y-cyclodextrin in aqueous solution. Adduct ions were not observed using these mctbods. ... 

Alhazmi,A., Giguere, M.S., Dube, M., Mayer, P.M. (2006) A comparison of electrospray-ionization and matrix-assisted laser desoption/ionization (MALDI) mass spectrometry with NMR spectroscopy for the characterization of synthetic copolymers. Eur. J. Mass Spectrom., 12,301-310. 

Because of the advances in the gas-phase ionization of biomacromolecules, such as electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI), mass spectrometry (MS) has become a powerful tool for detection, identification, and structural analysis of proteins, peptides, and polynucleotides. The molecules ionized in a gas phase by these methods are subsequently analyzed by sector, quadrupole, ion-trap, or time-of-flight mass spectrometers. In particular, the MS systems consisting of ESI and triple-stage quadrupole (ESI/TSQ) or ion-trap (IT) mass spectrometry and MALDI time-of-flight (MALDl/TOF) mass spectrometry have been most widely applied to the field of protein chemistry for the accurate determination of molecular mass of proteins and peptides, determination of amino acid sequence, identification of proteins by peptide mass databases, and analysis of posttranslational modifications such as phosphorylation and glycosylation. In general, current techniques allow detenni-... 

Advances in mass spectrometry have made it a tool of exceptional power for analysis of large biomolecules. Electrospray ionization, MALDI, and other soft ionization techniques for nonvolatile compounds and macromolecules make possible analyses of proteins, nucleic acids, and other biologically relevant compounds with molecular weights up to and in excess of 100,000 daltons. Electrospray ionization with quadrupole mass analysis is now routine for biomolecule analysis as is analysis using MALDI-TOF instruments. Extremely high resolution can be achieved using Fourier transform-ion cyclotron resonance (FT ICR, or FTMS). We shall discuss ESI and MALDI applications of mass spectrometry to protein sequencing and analysis in Sections 24.5E, 24.13B, and 24.14. 

Klushin DV, Gusev MY, Lysenko SA, Urazgildin IF. Phys Rev B 1996 54 7062. Knochenmuss R. In Cole R, editor. MALDI Ionization Mechanisms An Overview (Chapter 5) in Electrospray and MALDI Mass Spectrometry Fundamentals Instrumentation Practicalities and Biological Applications. 2nd ed. New York Wiley and Sons 2010. 

Electrospray ionization (ESI) mass spectrometry (MS) and matrix assisted laser desorption ionization (MALDI) have emerged recently as a powerful and sensitive methods for the detection and structural analysis of a wide variety of analytes, including large biomolecules such as nucleic acids and proteins. ESI-MS is a gentle method of ionization based on protonation of the sample at atmospheric pressure. The protonation of multiple basic sites in protein molecules results in multiply... 

Three techniques have been mainly utilized to characterize gold clusters, namely mass spectroscopy, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and extended X-ray absorption fine structure spectroscopy (EXAFS). For unsupported gold clusters, electrospray ionization (ESI) mass spectrometry and matrix-assisted laser desorption ionization (MALDI) mass... 

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). 

With the identities and amounts of amino acids known, the peptide is sequenced to find out in what order the amino acids are linked together. Much peptide sequencing is now done by mass spectrometry, using either electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALDI) linked to a time-of-flight (TOF) mass analyzer, as described in Section 12.4. Also in common use is a chemical method of peptide sequencing called the Edman degradation. 

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. 

Peptide mass fingeiprinting (PMF) is a mass spectrometry based method for protein identification. The protein is cleaved by an enzyme with high specificity (trypsin, Lys-C, Asp-N, etc.) or chemical (CNBr). The peptide mixture generated is analyzed by matrix-assisted laser desorp-tion/ionization (MALDI) or electrospray ionization (ESI)... 

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. 

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... 

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