Mass spectrometers description

The basic principles of fast-atom bombardment (FAB) and liquid-phase secondary ion mass spectrometry (LSIMS) are discussed only briefly here because a fuller description appears in Chapter 4. This chapter focuses on the use of FAB/LSIMS as part of an interface between a liquid chromatograph (LC) and a mass spectrometer (MS), although some theory is presented. 

The quadrupole mass spectrometer has been found to be particularly suitable for EGA in thermal analysis. Published reports include descriptions of the various systems used [153—155] and applications in studies of the pyrolysis of polymers [155], minerals [156] and many inorganic solids [157—159]. 

The apparatus used, as described previously (7), has modifications as described by Maier (16). A description also appears in this volume (15). A mass spectrometer of special design with 2-inch round poles, using 90° deflection with 1-inch magnetic radius, provides momentum-selected beams of low energy ions. These ions proceed at full energy... 

The present description is based on previous publications from this laboratory56-59 and the interested reader will find additional details and references in that work. Two different ion-source reaction chambers are used. One of these sources which operates at room temperature is shown in Figure 4. The second source, a variable temperature source will also be described. The electrospray generator and the ion-source reaction chamber are shown in Figure 4, while the mounting of the ion source and the front end of the mass spectrometer are shown in Figure 5. 

A mass spectrometer is often indispensable for a complete analysis of low-pressure gases, but a description of the various types of spectrometers is beyond the purpose of this book, but see, for example, ref. [18]. We simply remind that a mass spectrometer consists of three parts an ion source where the neutral gas is ionized (usually by electron bombardment) an analyser where ions are selected according to their mass to charge ratio and a collector with an amplifier to measure the weak ion current. 

A simple convention for description of peptide fragments formed in the mass spectrometer was proposed by Roepstorff and Fohlman in 1984 [1] and further modified by Johnson in 1987 [2]. Fragment ions are described by single lower-case letters with additional indexes (Fig. 6.5). If we consider fragmentation of a peptide backbone only, six ion series can be formed due to fragmentation at ... 

Description of several types of mass spectrometers used as detectors for GC. 

Srinivas, R. Stilzle, D. Weiske, T. Schwarz, H. Generation and Characterization of Neutral and Cationic 3-Silacyclopropenylidene in the Gas Phase. Description of a New BEBE Tandem Mass Spectrometer. Int. J. Mass Spectrom. lonProc. 1991,107, 369-376. 

Multi-collection mass spectrometers can analyze isotope ratios in a static mode to eliminate the errors from beam instability. However, the static multi-collection method depends on the extent to which the collectors (e.g., Faraday cups) are identical and to the extent to which the gain of each collector is stable. An alternative approach is to use the so-called dynamic multi-collector mode, to cancel out beam instability, detector bias, and performing a power-law mass fractionation correction. The following descriptions are modified from the Finnigan MAT 262 Operating manual (Finnigan, 1992). 

This textbook provides an overview of biomedical mass spectrometry with particular emphasis on GC/MS and quantitative methods. In addition, descriptions are provided of the various types of mass spectrometers and ionization techniques that are used for biomedical applications. 

A variety of experimental techniques have been used for the determination of uptake coefficients and especially Knudsen cells and flow tubes have found most application [42]. Knudsen cells are low-pressure reactors in which the rate of interaction with the surface (solid or liquid) is measured relative to the escape through an aperture, which can readily be calibrated, thus putting the gas-surface rate measurement on an absolute basis. Usually, a mass spectrometer detection system monitors the disappearance of reactant species, as well as the appearance of gas-phase products. The timescale of Knudsen cell experiments ranges from a few seconds to h lindens of seconds. A description of Knudsen cell applied to low temperature studies is given [66,67]. 

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