Electron bombardment mass

The isotopic ratios, altered by spike additions, are then measured on a portion of the sample by mass spectrometry. Even though the method is limited to elements having two or more naturally occurring or long lived isotopes, it is very sensitive and accurate and relatively free from interference effects. Thus, it has a great advantage over other analytical techniques. Thermal source and electron bombardment mass spectrom-... 

Electron bombardement mass spectrometry 200 Mg Lead tetramethyl Collins et al (1951) Kollar et al (1960) Ulrych and Russell (1964)... 

In addition, especially in the processed urushi samples, peaks with masses [M]K" =665 daltons and [M]K" =667 daltons which are the expected products of the dimerization reaction by oxidation of the phenol part of the catechol derivatives of urushiol. Supercritical fluid chromatography in combination with electron bombardment mass spectrometry was then used for the identification of some of the major components of the urushiol samples. Most prominently were found the trienes with [M]=314 daltons, and [M]=317 daltons and the monoenes. Again the compound with the mass of [M]=332 daltons was noticed which was the water adduct of the triene [M]=314 daltons. 

When subjected to an electron bombardment whose energy level is much higher than that of hydrocarbon covalent bonds (about 10 eV), a molecule of mass A/loses an electron and forms the molecular ion, the bonds break and produce an entirely new series of ions or fragments . Taken together, the fragments relative intensities constitute a constant for the molecule and can serve to identify it this is the basis of qualitative analysis. 

If the molecules could be detected with 100% efficiency, the fluxes quoted above would lead to impressive detected signal levels. The first generation of reactive scattering experiments concentrated on reactions of alkali atoms, since surface ionization on a hot-wire detector is extremely efficient. Such detectors have been superseded by the universal mass spectrometer detector. For electron-bombardment ionization, the rate of fonnation of the molecular ions can be written as... 

Unfortunately, not every compound shows a molecular ion in its mass spectrum. Although M+ is usually easy to identify if it s abundant, some compounds, such as 2,2-dimelhylpropane, fragment so easily that no molecular ion is observed (Figure 12.3). In such cases, alternative "soft" ionization methods that do not use electron bombardment can prevent or minimize fragmentation. 

Hydroxylamine, NHjOH, is subjected to electron bombardment The products are passed through a mass spectrograph. The two pairs of lines formed indicate charge/mass ratios of 0.0625,0.0588 and 0.1250,0.1176. How can this be interpreted ... 

Inghram and Corner showed that the mass spectra of molecules were much simpler using a field ionization source than with an electron bombardment ion source. Mainly parent ions are formed, unlike under electron impact which gives rise to considerable fragmentation. The simplicity of the mass spectra offers obvious applications in analysis of complex organic mixtures and their use is likely to become widespread... 

The first step in the application of mass spectra is obviously to obtain a list of fragment ions formed by electron bombardment of the molecule under study and their relative amounts by appropriate techniques. The goal from this point will necessarily be to relate the positive ions to the molecular structure whether it be an unknown structure to be identified, or a known structure of which a knowledge of fragmentation is desired. The fragment ions observed indicate the pieces of which the molecule is composed... 

One of the major limitations of FI is that the excess energy imparted to the analyte molecule during electron bombardment may bring about such rapid fragmentation that the molecular ion is not observed in the mass spectrum. Under... 

A differential vapour-pressure technique has been used to determine the molecular weights of phosphonic and phosphinic acids in 95% ethanol. Cryoscopic and n.m.r. studies have been made on solutions of phosphinic acids in sulphuric acid and oleum. Mass spectrometry has indicated the ready formation of phosphinylium ions after electron bombardment of phosphonic and phosphinic acids and their derivatives. However, the cryoscopic results in sulphuric acid indicated that reaction did not proceed beyond protonation, and the n.m.r. study on oleum solutions suggested that sulphonation occurred. 

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. 

Microprobe laser desorption laser ionisation mass spectrometry (/xL2MS) is used to provide spatial resolution and identification of organic molecules across a meteorite sample. Tracking the chemical composition across the surface of the meteorite requires a full mass spectrum to be measured every 10 p,m across the surface. The molecules must be desorbed from the surface with minimal disruption to their chemical structure to prevent fragmentation so that the mass spectrum consists principally of parent ions. Ideally, the conventional electron bombardment ionisation technique can be replaced with an ionisation that is selective to the carbonaceous species of interest to simplify the mass spectrum. Most information will be obtained if small samples are used so that sensitivity levels should be lower than attomolar (10—18 M) fewer than 1000 molecules can be detected and above all it must be certain that the molecules came from the sample and are not introduced by the instrument itself. 

Ionization and fragmentation of materials by a variety of means, principally by electron bombardment, or the softer techniques of chemical ionization, field ionization or fast atom bombardment. Analysis of the range of mass fragments produced. Elemental composition of non-volatile materials by application of an RF spark. 

Note. Abbreviations g.l.c., gas-liquid chromatography e.i.-m.s., electron-impact mass spectrometry c.i.-m.s., chemical-ionization mass spectrometry h.p.l.c., high-performance liquid chromatography h.p.a.e., high pH anion-exchange f.a.b.-m.s., fast-atom-bombardment mass spectrometry l.s.i.-m.s., liquid secondary-ion mass spectrometry n.O.e., nuclear Overhauser enhancement. Details of these methodologies are given in Ref. (3). 

The formation of gaseous organic cations under electron bombardment of alkanes, haloalkanes and other precursors has been widely investigated in mass spectral studies (Field and Franklin, 1957 McLafiFerty, 1963). 

Cameron, A.E. Electron-Bombardment Ion Source for Mass Spectrometry of Solids. Rev. Sci. Instrum. 1954, 25, 1154-1156. 

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