Modern mass spectrometer

Modern mass spectrometers are interfaced with computerized data handling sys terns capable of displaying the mass spectrum according to a number of different for mats Bar graphs on which relative intensity is plotted versus m z are the most common Figure 13 40 shows the mass spectrum of benzene m bar graph form... 

Which directs them toweurds the analyzer slits. Alternatively, they may be extracted by the field penetration of the high voltage on the focusing electrodes. In both instances the ion beam is usually focused, collimated and accelerated to provide a beam of narrow energy dispersion that is capable of traversing the analyzer section of the mass spectrometer. In modern mass spectrometers the ionization source and analyzer sections are usually differentially pumped, allowing the source to operate at a distinctly higher... 

Several Interface designs are available for GC/MS and selection depends on the circumstances of the experiment [3-6,8,25,26]. Column flow rates of 1-2 ml/min (adjusted to STP) into the ion source are compatible with modem mass spectrometer vacuxim systems. This is also the optimum floi te range for open tubular capillary columns of conventional lensions. Coupling such columns to a modern mass spectromet er, therefore, presents... 

The extensive research on nitro compounds confirms a rich gas-phase ion chemistry. It is, however, noteworthy that Porter, Beynon and Ast in the classical review, The Modern Mass Spectrometer—A Complete Chemical Laboratory, were able to demonstrate the capabilities of mass spectrometry with no less than thirty different experiments involving a single compound, i.e. nitrobenzene1. 

The sensitivity of modern mass spectrometers enables subsequent employment of micro reactions even if the yields per step are only moderate. Here an... 

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.

Modern mass spectrometers are so precise that molecular masses can often be measured to seven significant figures. A 12Ci01H8 molecule of naphthalene, for example, has a molecular mass of 128.0626 amu as measured by mass spectrometry. 

Modern mass spectrometers make it possible for substances in the femtomole range (10-15M) to be analyzed, and for high molecular masses of complex molecules well over 100 kDa to be obtained. Mass spectrometers allow molecular mass determination, and the generation of fragmentation data to allow sequencing and structure elucidation, generally in tandem mass-spectrometric experiments. 

The goal of Chapter 6 is to familiarize investigators in biological and medical research with mass spectrometry and its potential applications in these fields, with the anticipation that it will encourage and enable them to utilize MS in their research. An attempt has been made to provide a clear basic description of the modern mass spectrometers and of the most relevant types of experiments that they can perform. Discussed also are the advantages and drawbacks of the different methods in the context of biological research with examples of the ability of mass spectrometry to solve problems in this field of research. 

Atomic masses are so small that an appropriate unit was developed to report them—an atomic mass unit (amu). 1 amu = 1.66 x 10 " g. The atomic mass of the lightest element, hydrogen, was originally taken to be 1 amu. The modern values of the atomic masses are based on the most common kind of carbon atom, called carbon-12 and written as the standard. The mass of is measured in the modern mass spectrometer, and is defined to have an atomic mass of exactly 12 amu. On this scale hydrogen has an atomic mass of 1.008 amu. 

The sensitivity and quality of data available from modern mass spectrometers mean that the preparation of samples is one of the main limitations in many proteomic protocols. 

Figure 5-10 shows a modern mass spectrometer. In nature, some elements, such as fluorine and phosphorus, exist in only one form, but most elements occur as isotopic mixtures. Some examples of natural isotopic abundances are given in Table 5-3. The percentages are based on the numbers of naturally occurring atoms of each isotope, not on their masses. 

Figure S-10 (a) A modern mass spectrometer, (b) The mass spectrum of Xe+ ions. The isotope 54Xe is at too low an abundance (0.090%) to appear in this experiment.

Modern mass spectrometer systems rely heavily on integrated computer control systems for instrument control, data collection, and data processing. Whereas... 

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