Fast atom bombardment high-mass analytes

Fast-atom bombardment (FAB) is one of a number of ionization techniques which utilize a matrix material, in which the analyte is dissolved, to transfer sufficient energy to the analyte to facilitate ionization. In FAB, the matrix material is a liquid, such as glycerol, and the energy for ionization is provided by a high-energy atom (usually xenon) or, more recently, an ion (Cs+) beam. In conventional FAB, the solution of analyte in the matrix material is applied to the end of a probe which is placed in the source of the mass spectrometer where it is bombarded with the atom/ion beam. 

MS involves the separation of ions based on their mass-to-charge ratio (m/z). The concept was invented a century ago1 with a dramatic impact on analytical chemistry.2-3 The fundamental principle of MS requires vaporization of the molecules in the gas phase and in ionization. Early ionization methods such as electron impact (El) and chemical ionization (Cl)4-5 were limited to small organic molecules that were volatile and stable to heat and amenable to transfer into high vacuum. Introduction of the fast-atom-bombardment (FAB) method of ionization6... 

If high-resolution measurements are performed in order to assign elemental compositions, internal mass calibration is almost always required. The calibration compound can be introduced from a second inlet system or be mixed with the analyte before the analysis. Mixing calibration compounds with the analyte requires some operational skills in order not to suppress the analyte by the reference or vice versa. Therefore, a separate inlet to introduce the calibration compound is advantageous. This can be achieved by introducing volatile standards such as PFK from a reference inlet system in electron ionization, by use of a dual-target probe in fast atom bombardment, or by use of a second sprayer in electrospray ionization. 

Fast atom bombardment mass spectrometry (FABMS) has become an important addition to the ionization techniques available to the analytical chemist in recent years. It has been particularly useful in a number of diverse applications which include molecular weight determinations at high mass, peptide and oligosaccharide sequencing, structural analysis of organic compounds, determination of salts and metal complexes, and the analysis of ionic species in aqueous solutions. This paper will focus on some aspects of the quantitative measurement of ionic species in solution. The reader is referred to a more comprehensive review for more details of some of the examples given here as well as other applications (1). 

Several interfaces have been used for CCC-MS (mass spectrometry). The first employed is thermospray (TSP). When a column is directly coupled with TSP MS, the CCC column often breaks due to the high back-pressure generated by the thermospray vaporizer. By contrast, other interfaces, such as fast atom bombardment (FAB), electron ionization (El), and chemical ionization (Cl), have been directly connected to a CCC column without generating high back-pressure. Such interfaces can be applied to analytes with a broad range of polarities. As it is suitable to introduce effluent from the column CCC into MS at a flow rate of only between 1 and 5 L/min, the effluent is usually introduced into the MS through a splitting tee, which is adjusted to an appropriate ratio. 

We report on the further physical and chemical characterization of the new forms of molecular carbon, C ) and C70. Our results demonstrate a high yield of production (14%) under optimized conditions and reveal only and C70 in measurable quantity, in an 8S IS ratio. These two new molecular forms of carbon can be completely separated in analytical amounts by column chromatography on alumina. Comparison among mass spectra obtained by the electron impact, laser desorption, and fast atom bombardment (FAB) methods allows a clear assessment of the composition of the mixed and pure samples, and of the fragmentation and double ionization patterns of the molecules. In addition, spectroscopic analyses are reported for the crude mixture by C NMR and by IR spectroscopy in KBr pellet, and for pure C o and C70 in solution by UV-vis spectroscopy. 

This paper describes the further physical and chemical characterization of these two new forms of molecular carbon." Our results include the high-yield production (14%) of soluble material under optimized conditions, consisting of only C o and C70 in measurable quantity. These have been separated in analytical amounts by column chromatography and have been characterized in pure or mixed forms by a combination of electron impact, fast atom bombardment (FAB), and laser desorption mass spectrometry. Spectroscopic characterization is reported including the C NMR spectrum and the infrared absorption spectrum for the crude... 

Other Methods of Ionization. There are several other methods for ionization in addition to ESI and MALDI. However, most of them are not commonly used in proteomics. Some of these include chemical ionization, electron ionization, fast atom bombardment (FAB), and many others. Most of these lead to disintegration or fragmentation of analyte molecules and are not commonly used in proteomics. However, FAB has some application in the analysis of proteins and peptides, because this is a soft ionization procedure and does not cause the fragmentation of molecules under analysis. In the FAB method, a nonvolatile matrix such as m-nitrobenzyle alcohol is used to hold the analyte molecules. Analyte molecules are vaporized and ionized by bombardment with the high-energy beam of xenon or cesium from a probe inserted directly into the device containing the sample. Ionized molecules thus obtained are then subjected to separation by the mass... 

A variety of volatilization/ionization methods have been applied to polymers a recent review or key paper is cited here for each. Extensive reviews that include mass spectrometry of pol5mrers can be found in Analytical Chemistry Other to )ical reviews are field desorption, laser desorption, plasma desorption, fast-atom bombardment, pyrolysis, and electrospray ionization. The present review will focus on polymer characterization using secondary-ion mass spectrometry (SIMS) in the high mass range comparison with other methods will be presented where appropriate. 

Henzel WJ, Bourell JH, and Stubs JT (1990) Analysis of protein digests by capillary high-performance liquid chromatography and on-line fast atom bombardment mass spectrometry. Analytical Biochemistry 187 228. 

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