Electron impact mass spectrometer

A number of excellent reviews and books have included consideration of the fundamental electron impact ionization process, and the attention afforded the experimental measurement of ionization potentials and Augment ion appearance energies over the years is reflected in the comprehensive database of ionization potentials and gas phase ion enthalpies of formation published through the National Bureau of Standards in printed and electronic forms. In contrast, few absolute ionization cross sections have been measured. The most comprehensive compilation of molecular ionization cross sections are relative values measmed with a modified commercial electron impact mass spectrometer ion source using the cross section for Ar as a reference. ... 

Electron impact mass spectrometers are generally set up to detect only positive ions, but negative-ion mass spectrometry is also possible. 

Figure 4.1 Schematic Diagram of an Electron-Impact Mass Spectrometer...

Another type of IR gas-sensor has been reported by Cong et al. for the HTS of ethane ODH [12, 13]. They used a photothermal deflection (PTD) detector with a mass spectrometer because an electron-impact mass spectrometer cannot detect C2H4 concentrations at the ppm level in the presence of high concentrations of... 

Ionization and fragmentation produce a mixture of particles, some neutral and some positively charged. To understand what follows, we need to examine the design of an electron-impact mass spectrometer, shown in a schematic diagram in Figure 13.34. The sample is bombarded with 70-eV electrons, and the resulting positively charged ions (the... 

There is no doubt that many devices are superior to the single-source, electron-impact mass spectrometer for physiochemical measurements. In fact, the instrument has been declared obsolete for at least fifteen years. Yet, for all this, it continues to find extensive use and probably will continue to do so for many years. 

Bose AK, Pramanik BN, Bartner PL. Mass spectral studies. Part 120. Facile ionization induced by ammonium salts Mass spectra of nonvolatile compounds using unmodified electron-impact mass spectrometers. J Org Chem 1982 47 4008-4010. 

Not only the product angular distribution can be determined, but also its recoil velocities. This type of measurement, i.e. both the angular and velocity distribution of the reaction products, is currently made using the universal crossed-beam technique in which a rotatable electron-impact mass spectrometer is used... 

Figure 21,9 Universal crossed-beam apparatus with a rotatable electron-impact mass spectrometer, following the design of Lee et al. (1969). Adapted from Casavecchia, Rep. Prog. Phys., 2000, 63 355, with permission of lOP...

Figure 2. Low resolution (/ = 1000) spectrum of dehydro-epi-androsteron. direct inlet using a VG 7070E. electron impact mass spectrometer (ElMS)...

The ion source. In an electron impact mass spectrometer, a sample of the compound is bombarded by electrons. The collision of a high-energy electron with a sample molecule converts it into a radical cation. 

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