Ionization electron beams

Sodium valproate was not sufficiently volatile for mass spectral analysis. The mass spectrum of valproic acid as shown in Figure 5 was obtained using an Associated Electrical Industries Model MS-902 Mass Spectrometer with the ionization electron beam energy at 70 eV. High resolution data were compiled and tabulated with the aid of an on-line PDP-11 Computer. 

Employing a direct exposure probe (DEP) may be helpful in case of analytes that cannot be evaporated from a sample vial without complete decomposition. [44] Here, the analyte is applied from solution or suspension to the outside of a thin wire loop or pin which is then directly exposed to the ionizing electron beam. This method has also been termed in-beam electron ionization. Early work describing the direct exposure of a sample to the electron beam came from Ohashi, [45,46] Constantin, [47] and Traldi. [48,49]... 

The mass spectra of atenolol and compound were obtained by direct insertion of the sample into CEC 21-Ho B mass spectrometer. Characteristics of these mass spectra are summarized in Tables 5. and 6, and Pig. 5 The ion source temperature was 15o°C and 2oo-25o°C, respectively, and the ionizing electron beam energy was 7o eV. 

Many other aliphatic or aromatic amines produce the same reaction. However if N-alkyl (or aryl)2-aniline is made to react with tris-dimethylaminophosphine, tricoordinated phosphorus compounds are obtained. Their analyses and mass spectra show that they are tetramers (5) when the energy of the ionizing electron beam is nearly 70 eV the mass spectra of the oligomers show an intense [M] peak which corresponds to the monomer ion (n = 1) but when the spectra are obtained by field desorption m.s. the molecular ion peak corresponds to a tetramer (n = 4) one sees also smaller peaks for ions n = 3, 2 or 1. 

Using ionizing radiation for intramolecular cross-linking of individual polymers, the synthesis can be performed in the absence of additional initiators, cross-linkers, or additives. For this approach, a pure aqueous solution of the polymer is exposed to a short intense pulse of ionizing electron beam radiation (typically a few microseconds, see Sect. 2.3, Fig. 1). During the exposure many radicals are generated simultaneously along each polymer chain. The intramolecular recombination of these... 

Direct introduction probe. The solid sample to be analysed is placed in a gold or glass crucible at the tip of a probe which can be introduced through a vacuum lock into close proximity with the ionizing electron beam. The temperature of the probe tip is controlled to maintain a steady evaporation rate of the sample. 

Wyeth Lot No. F-665901) was obtained- -- - by direct insertion of the sample into an MS-902 double focusing mass spectrometer. Results are summarized as a bar graph (Figure U). The ion source temperature was ll 0°C. and the ionizing electron beam energy was 70 eV. Data were compiled by Kuhlman and Shrader- - with the aid of an on-line PDP 8 Digital Computer. 

A target may resist hydrolysis or chemical degradation, or the degradation products may not yield useful information. It is also common that insufficient material exists for proper analysis. In these cases, an alternative degradation technique is available that uses the ionizing electron beam of a mass spectrometer. The ionization pathways available from electron impact in the mass spectmm are bond fission processes that occur by known and predictable pathways. Indeed, each pathway usually follows analogous chemical reaction pathways in a retro-synthetic manner. It therefore follows that an examination of mass spectral ionization patterns can give clues for suitable disconnections and a synthetic tree. 

One method of confirming that a particular peak corresponds to a molecular ion is to vary the energy of the ionizing electron beam. If the energy of the beam is lowered, the tendency of the molecular ion to fragment lessens. As a result, the intensity of the molecular ion peak should increase with decreasing electron potential, while the intensities of the fragment ion peaks should decrease. 

Direct Probe Analysis. In the direct inlet (direct probe or solids probe) MS technique, the sample is placed in a small cup and inserted into the ion source a few millimeters from the ionizing electron beam (Figure 4). The cup is heated so that solids or liquids of low volatility can be directly vaporized into the electron beam. Only 10" to 10" ... 

The (details of these measurements are beyond the scope of this text Because they require an ionizing electron beam, measured proton afhnities d gas-[ ase basicities fcx many species have large uncertainties, because the molecules involved frequently are in excited states (with excess energy above their ground states), and some species do not yield the necessary acid as a gaseous fragment Relatively few molecules are ideally suited f[Pg.177]

Flexible rubber Rubber Made by mixing natural rubber, rehydrated precipitated silica. This is then extruded and calendared, irradiated with an ionizing electron beam and dried. Flexible, fine pore stracture (0.06 pm average), retards antimony transfer... 

Cameron and Eggers introduced their velocitron, an instrument with a Nier electron impact source, a 317-cm drift tube, and oscilloscope recording. Ions were accelerated to a constant energy of 500 eV, so that their velocities would be inversely proportional to the square root of their masses. The 1955 instrument by Katzenstein and Friedland pulsed both the ionizing electron beam and the ion extraction field, using a drawout (orpushout) pulse. A pulsed extraction approach was also developed by Wiley and McLaren as ameans to improve mass resolution. Their instrument was commercialized, and their approach is the forerunner of the current delayed extraction methods used in MALDl. 

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