Ionization methods, for mass spectrometry

Metastable atom bombardment (MAB) is a novel ionization method for mass spectrometry invented by Michel Bertrand s group at the University of Montreal, Quebec, Canada, and described by Faubert et al.38 For the identification of bacteria by MS, MAB has a number of significant advantages relative to more familiar ionization techniques. Electron ionization (El) imparts so much excess energy that labile biomolecules break into very small fragments, from which the diagnostic information content is limited since all... 

Atmospheric pressure photoionization (APPI) was recently introduced in the world of atmospheric pressure ionization techniques to analyze nonpolar molecules that are not efficiently ionized either by ESI or by APCI. Photoionization (PI) was already exploited some 30 years ago as a detection method for GC and LC, but only in recent times it has been used as an ionization method for mass spectrometry [52],... 

Peptides. One of the applications that has benefited most from the development of soft ionization methods for mass spectrometry has been the analysis of polar biological materials. Peptides, in particular, have been extensively studied by a variety of soft ionization methods, primarily FAB, with excellent results being obtained for peptides in the 1000-10000 dalton range. LD-FTMS also has proved to be very successful for analysis of simple peptides and an examination of these results should help delineate the analytical potential of LD-FTMS in this important area. 

G. J. Van Berkel, An overview of some recent developments in ionization methods for mass spectrometry, Eur. J. Mass Spectrom. 9 (2003), 539-562. 

Shiokawa Y, Nakamura M, Hirano Y, Fujii T. Ionization apparatus and ionization method for mass spectrometry. From U.S. Pat Appl Publ. 2002 US 20020053636 A1 20020509, Language English. 

Grotemeyer J, Boesl U, Walter K and Schlag EW (1986) A general soft ionization method for mass spectrometry resonance-enhanced multiphoton ionization of biomolecules. Organic Mass Spectrometry 21 645-653. 

Nobel Prize in Chemistry 2002 to John B. Fenn and Koichi Tanaka (and Kurt Wiithtich for NMR structure analyses of biological macromolecules ) for their development of soft desorption ionization methods for mass spectrometry. ... 

Electrospray (ESI) is an atmospheric pressure ionization source in which the sample is ionized at an ambient pressure and then transferred into the MS. It was first developed by John Fenn in the late 1980s [1] and rapidly became one of the most widely used ionization techniques in mass spectrometry due to its high sensitivity and versatility. It is a soft ionization technique for analytes present in solution therefore, it can easily be coupled with separation methods such as LC and capillary electrophoresis (CE). The development of ESI has a wide field of applications, from small polar molecules to high molecular weight compounds such as protein and nucleotides. In 2002, the Nobel Prize was awarded to John Fenn following his studies on electrospray, for the development of soft desorption ionization methods for mass spectrometric analyses of biological macromolecules. ... 

The application of molecular SIMS as a sensitive ionization source for nonvolatile and thermally labile molecules compares favorably with other new ionization methods in mass spectrometry such as field desorption (FD), Californium-252 plasma desorption (PD), fast heavy ion induced desorption (FHIID), laser desorp-... 

Ionization Methods/Processes. The recent development of several new ionization methods in mass spectrometry has significantly improved the capability for the analysis of nonvolatile and thermally labile molecules [18-23]. Several of these methods (e.g., field desorption (FD), Californiun-252 plasma desorption (PD), fast heavy ion induced desorption (FHIID), laser-desorption (LD), SIMS, and fast atom bombardment (FAB) or liquid SIMS) desorb and ionize molecules directly from the solid state, thereby reducing the chance of thermal degradation. Although these methods employ fundamentally different excitation sources, similarities in their mass spectra, such as, the appearance of protonated, deprotonated, and/or cationized molecular ions, suggest a related ionization process. 

Laser Desorption Ionization. A pulsed laser beam can be used to ionize samples for mass spectrometry. Because this method of ionization is pulsed, it must be used with either a time of flight or a Fourier transform mass spectrometer (Section 1.4.5). Two types of lasers have found widespread use A COz laser, which emits radiation in the far infrared region, and a frequency-quadrupled neodymium/yttriumaluminum-garnet (Nd/YAG) laser, which emits radiation in the UV region at 266 nm. Without matrix assistance, the method is limited to low molecular weight molecules (<2 kDa). 

Remarkably, however, textbooks on mass spectrometry hardly comprise the multifaceted aspects of the gas-phase ion chemistry of phenols and of their consequences for the characteristics of the mass spectra of phenolic compounds . A great many insights into the fundamentals and developments for analytical applications have been collected during the past four decades or so, and research is actively continued in this field. As a special circumstance, a number of phenolic compounds play a crucial—and yet not completely understood—role as energy-transferring media and protonating reagents in an extremely important, modern ionization method of mass spectrometry, viz. matrix-assisted laser desorption/ionization (MALDI) . ... 

Nearly all known ionization methods of mass spectrometry (including electron impact, laser desorption and fast atom bombardment) were already successfully applied to lipids. However, many ionization techniques are not very suitable for the analysis of complex PL mixtures as they provide considerable amounts of fragment ions. Therefore, only three soft-ionization methods play nowadays a major role in lipid analysis. Beside atmospheric pressure chemical ionization (APCI) (Byrdwell 2001), electrospray ionization (ESI) (Pulfer and Murphy... 

In the past several years, a number of new ionization methods in mass spectrometry have been introduced. These new techniques have extended mass spectrometric analysis to a wide variety of labile (thermally unstable), highly polar, and higher molecular weight materials. Field ionization (FI) and field desorption (FD) are two of the pioneering techniques in this list of alternative ionization methods. FI-MS, which was introduced for organic molecules in 1954, was the first soft ionization method. (Soft ionization refers to processes that produce high relative abundances of molecular, or quasimolecular, ions.) FD-MS, which was invented in 1969, was the first desorption/ionization method. (Desorption/ionization refers to processes in which die vaporization/ desorption, and ionization steps occur essentially simultaneously.)... 

To date, no fewer than five Nobel Prizes have been awarded for work directly related to mass spectrometry J. J. Thomson (Physics, 1906) for theoretical and experimental investigations on the conduction of electricity by gases F. W. Aston (Chemistry, 1922) for discovery, by means of a mass spectrograph, of isotopes, in a large number of nonradioactive elements W. Paul (Physics, 1989) for the development of the ion trap technique and most recently J. B. Fenn and K. Tanaka (Chemistry, 2002) for the development of soft desorption ionization methods for mass spectrometric analyses of biological macromolecules. ... 

Aerosols can be produced as a spray of droplets by various means. A good example of a nebulizer is the common household hair spray, which produces fine droplets of a solution of hair lacquer by using a gas to blow the lacquer solution through a fine nozzle so that it emerges as a spray of small droplets. In use, the droplets strike the hair and settle, and the solvent evaporates to leave behind the nonvolatile lacquer. For mass spectrometry, a spray of a solution of analyte can be produced similarly or by a wide variety of other methods, many of which are discussed here. Chapters 8 ( Electrospray Ionization ) and 11 ( Thermospray and Plasmaspray Interfaces ) also contain details of droplet evaporation and formation of ions that are relevant to the discussion in this chapter. Aerosols are also produced by laser ablation for more information on this topic, see Chapters 17 and 18. 

This article discusses why one would choose nonresonant multiphoton ionization for mass spectrometry of solid surfaces. Examples are given for depth profiling by this method along with thermal desorption studies. 

Electrospray ionization mass spectrometry (ESI-MS) is an analytical method for mass determination of ionized molecules. It is a commonly used method for soft ionization of peptides and proteins in quadmpole, ion-trap, or time-of-flight mass spectrometers. The ionization is performed by application of a high voltage to a stream of liquid emitted from a capillaty. The highly charged droplets are shrunk and the resulting peptide or protein ions are sampled and separated by the mass spectrometer. 

Separation and detection methods The common methods used to separate the Cr(III)/(VI) species are solvent extraction, chromatography and coprecipitation. In case of Cr(VI) from welding fumes trapped on a filter, a suitable leaching of the Cr(VI) from the sample matrix is needed, without reducing the Cr(VI) species. The most used detection methods for chromium are graphite furnace AAS, chemiluminescence, electrochemical methods, ICP-MS, thermal ionization isotope dilution mass spectrometry and spectrophotometry (Vercoutere and Cornelis 1995)- The separation of the two species is the most delicate part of the procedure. 

A second role for mass spectrometry in the investigation of reactive intermediates involves the nse of spectroscopy. Althongh an important nse of ion spectroscopy is the determination of thermochemical properties, including ionization energies (addition or removal of an electron), as in photoelectron or photodetachment spectroscopy, and bond dissociation energies in ions, as in photodissociation methods, additional spectroscopic data can also often be obtained, inclnding structural parameters such as frequencies and geometries. 

In a separate study, a protocol for Matrix-assisted laser desorption-ionization (MALDI) imaging mass spectrometry (IMS) has been proposed.18 This IMS technique provides a new approach to visualize spatial distribution of thousands of molecular species, including peptides, proteins, and their metabolites in two- or three-dimensional levels. This approach may also provide a straightforward method of determining the tissue distribution of multiple peptides or proteins in a quantitative manner.18 Chu et al.19 reported a nondestructive molecular extraction method to obtain proteins from a single FFPE or frozen tissue section, without destroying the tissue morphology, such... 

D. R. Robb, T. R. Covey, and A. P. Bruins. Atmospheric Pressure Photoionization An Ionization Method for Liquid Chromatography-Mass Spectrometry. Anal. Chem., 72(2000) 3653-3659. 

It is the great advantage of APCI that it - different from ESI - actively generates ions from neutrals. Thus, APCI makes low- to medium-polarity analytes eluting from a liquid chromatograph accessible for mass spectrometry. In contrast to its development as an ionization method, the application of APCI has a backlog behind ESI. The use of APCI rapidly grew in the mid-1990, perhaps because... 

Robb, D. B., Covey, T. R., and Bruins, A. P. (2000). Atmospheric pressure photoionization an ionization method for liquid chromatography-mass spectrometry. Anal. Chem. 72, 3653 — 3659. 

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