Fast atom bombardment source

Fast Atom Bombardment Source a. ion gun b. charge exchange region d. exchange region gas admission port admission g. deflection electrode h. 

Figure 2.35 Schematic diagram of a fast atom bombardment source (Figure used by kind permission of Dr Paul Cates, School of Chemistry, University of Bristol, UK).

Mass spectra were obtained on a AEI MS9 (Manchester, U.K.) instrument equipped with a fast atom bombardment source (Figures 10 and 11). The medium was either glycerol or Cleland and the sample was introdiKxd by means of direct insertion. Instrument settings were 92-963 total scans in run, 4 sampling rate, 256 signal level threshold, 30 minimum peak width, 5 scan rate (sec/dec), 10.0. 

Caprioli, R.M. Beckner, C.F. Smith, L.A. Performance of a Fast-Atom Bombardment Source on a Quadrupole Mass Spectrometer. Biomed. Mass Spectrom. 1983,10, 94-97. 

Fig. 1. Schematic representation of a fast atom bombardment source...

A connnon feature of all mass spectrometers is the need to generate ions. Over the years a variety of ion sources have been developed. The physical chemistry and chemical physics communities have generally worked on gaseous and/or relatively volatile samples and thus have relied extensively on the two traditional ionization methods, electron ionization (El) and photoionization (PI). Other ionization sources, developed principally for analytical work, have recently started to be used in physical chemistry research. These include fast-atom bombardment (FAB), matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ES). 

Fast-atom bombardment (FAB) is one of a number of ionization techniques which utilize a matrix material, in which the analyte is dissolved, to transfer sufficient energy to the analyte to facilitate ionization. In FAB, the matrix material is a liquid, such as glycerol, and the energy for ionization is provided by a high-energy atom (usually xenon) or, more recently, an ion (Cs+) beam. In conventional FAB, the solution of analyte in the matrix material is applied to the end of a probe which is placed in the source of the mass spectrometer where it is bombarded with the atom/ion beam. 

Several other interface designs were introduced over this period, including continuous flow fast atom bombardment (CFFAB)" and the particle beam interface (PBI)," but it was not until the introduction of the API source that LC/MS applications really came to the forefront for quantitative analysis. Early work by Muck and Henion proved the utility of an atmospheric pressure interface using a tandem quadrupole mass spectrometer. 

Recent attention has focused on MS for the direct analysis of polymer extracts, using soft ionisation sources to provide enhanced molecular ion signals and less fragment ions, thereby facilitating spectral interpretation. The direct MS analysis of polymer extracts has been accomplished using fast atom bombardment (FAB) [97,98], laser desorption (LD) [97,99], field desorption (FD) [100] and chemical ionisation (Cl) [100]. 

The mass spectra of mixtures are often too complex to be interpreted unambiguously, thus favouring the separation of the components of mixtures before examination by mass spectrometry. Nevertheless, direct polymer/additive mixture analysis has been reported [22,23], which is greatly aided by tandem MS. Coupling of mass spectrometry and a flowing liquid stream involves vaporisation and solvent stripping before introduction of the solute into an ion source for gas-phase ionisation (Section 1.33.2). Widespread LC-MS interfaces are thermospray (TSP), continuous-flow fast atom bombardment (CF-FAB), electrospray (ESP), etc. Also, supercritical fluids have been linked to mass spectrometry (SFE-MS, SFC-MS). A mass spectrometer may have more than one inlet (total inlet systems). 

Principles and Characteristics In the early mass-spectrometric ionisation techniques, such as El and Cl, the sample needs to be present in the ionisation source in its gaseous phase. Volatilisation by applying heat renders more difficult the analysis of thermally labile and involatile compounds, including highly polar samples and those of very high molecular mass. Although chemical derivatisation may be used to improve volatility and thermal stability, many compounds have eluded mass-spectrometric analysis until the emergence of fast atom bombardment (FAB) [72]. 

The combination of CE with continuous-flow fast atom bombardment (CF-FAB-MS) requires the use of an interface, because of the incompatibility of the CF-FAB process and CE for liquid flow [888], The CF-FAB source requires a solvent, usually water/glycerol (95-5 v/v), which is maintained at a steady flow-rate of 2-15mLmin 1. Flow-rate in CE does not exceed 1 nLmin-1. 

R. S. Annan, H. J. Kochling, J. A. Hill, and K. Biemann. Matrix-Assisted Laser Desorption Using a Fast-Atom Bombardment Ion Source and a Magnetic Mass Spectrometer. Rapid Commun. Mass Spectrom., 6(1992) 298-302. 

More recently, attention has turned to the aftertreatment of commercially available mordant dyes on wool with iron(II) and iron(III) salts as a potential source reduction approach to eliminating chromium ions from dyebath effluent [34]- The anticipated improvements in fastness performance were achieved. The structures of the conventional 1 2 iron-dye complexes formed on the wool fibres were characterised by negative-ion fast-atom bombardment spectroscopy and HPLC analysis [35]. 

Mass spectrometry is traditionally a gas phase technique for the analysis of relatively volatile samples. Effluents from gas chromatographs are already in a suitable form and other readily vaporized samples could be fairly easily accommodated. However the coupling of mass spectrometry to liquid streams, e.g. HPLC and capillary electrophoresis, posed a new problem and several different methods are now in use. These include the spray methods mentioned below and bombarding with atoms (fast atom bombardment, FAB) or ions (secondary-ion mass spectrometry, SIMS). The part of the instrument in which ionization of the neutral molecules occurs is called the ion source. The commonest method of... 

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