Interface fast atom bombardment

The Continuous-Flow/Frit (Dynamic) Fast-Atom-Bombardment Interface... 

M. A. Moseley, L. J. Deterding, K. B. Tomer, and J. W. Jorgenson. Nanoscale Packed-Capillary Liquid Chromatography Coupled with Mass Spectrometry Using a Coaxial Continuous-Flow Fast Atom Bombardment Interface. Anal. Chem., 63(1991) 1467-1473. 

Moseley, M. A. Deterding, L. J. Tomer, K. B. Jorgenson, J. W. 1991. Nanoscale packed-capillary liquid chromatography coupled with mass spectrometry using a coaxial continuous-flow fast atom bombardment interface. Anal. Chem., 63,1467-1473. 

Over 30 years of liquid chromatography-mass spectrometry (LC-MS) research has resulted in a considerable number of different interfaces (Ch. 3.2). A variety of LC-MS interfaces have been proposed and built in the various research laboratories, and some of them have been adapted by instmment manufacturers and became commercially available. With the advent in the early 1990 s of interfaces based on atmospheric-pressure ionization (API), most of these interfaces have become obsolete. However, in order to appreciate LC-MS, one carmot simply ignore these earlier developments. This chapter is devoted to the older LC-MS interfaces, which is certainly important in understanding the histoiy and development of LC-MS. Attention is paid to principles, instrumentation, and application of the capillary inlet, pneumatic vacuum nebulizers, the moving-belt interface, direct liquid introduction, continuous-flow fast-atom bombardment interfaces, thermospray, and the particle-beam interface. More elaborate discussions on these interfaces can be found in previous editions of this book. 

Nanoscale LC for LC-MS was pioneered by Deterding et al. [52] using a coaxial continuous-flow fast-atom bombardment interface. Nano-LC was commercialized by LC Packings, both with respect to column technology and instrumentation [53]. Nowadays, nano-LC is available from several instrument and column manufacturers. 

Other Techniques. A growing technique related to lc/ms and regarded as complementary to it is that of capillary zone electrophoresis/mass spectrometry (cze/ms) (22). Using cze/ms, high resolution separation of water-soluble compounds is accompHshed by the principles of electrophoresis (qv). The sample is then coupled to the mass spectrometer by electrospray ionization (23) or a fast atom bombardment interface (fab) to produce molecular ions (24). Biotechnology applications of cze/ms have great potential (25). 

Continuous-Flow Fast Atom Bombardment Interface Although currently not a popular approach, the coupling of CE mass spectrometry was once achieved via a CF-FAB probe. Makeup flow is required in this coupling because of the mismatch of the low flow rates of the CE solution with the liquid flow rates of stable CF-FAB operation. The sheath-flow and liquid-junction designs discussed above have been used successfully for this purpose [69-71], The sheath-flow design has the advantages that the composition and the flow rates of the CE effluents and of the FAB matrix solution can be optimized independently, and that the separation efficiency is higher. 

In the past 10 years, the manner in which LC-MS analysis is performed has significantly changed. While in the past it was necessary to choose the most appropriate LC-MS interface for a particular application from a list of five possibilities, e.g., the moving-belt interface, the direct-liquid introduction interface, the thermospray interface, the particle-beam interface, and the continuous-flow fast-atom bombardment interface, today all LC-MS technologies are based on API. The two most important... 

Dynamic Fast-Atom Bombardment and Liquid-Phase Secondary Ion Mass Spectrometry (FAB/LSIMS) Interface... 

The basic principles of fast-atom bombardment (FAB) and liquid-phase secondary ion mass spectrometry (LSIMS) are discussed only briefly here because a fuller description appears in Chapter 4. This chapter focuses on the use of FAB/LSIMS as part of an interface between a liquid chromatograph (LC) and a mass spectrometer (MS), although some theory is presented. 

LC can be combined with all kinds of mass spectrometers, but for practical reasons only quadrapolar, magnetic/electric-sector, and TOP instruments are in wide use. A variety of interfaces are used, including thermospray, plasmaspray, electrospray, dynamic fast-atom bombardment (FAB), particle beam, and moving belt. 

The full potential of LC-MS could not be exploited until it was possible to study involatile and thermally labile compounds for which electron and chemical ionization are not appropriate. A relatively small number of reports of the use of the moving-belt interface with fast-atom bombardment ionization for the study of these types of compound have appeared. 

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. 

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). 

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. 

In off-line coupling of LC and MS for the analysis of surfactants in water samples, the suitability of desorption techniques such as Fast Atom Bombardment (FAB) and Desorption Chemical Ionisation was well established early on. In rapid succession, new interfaces like Atmospheric Pressure Chemical Ionisation (APCI) and Electrospray Ionisation (ESI) were applied successfully to solve a large number of analytical problems with these substance classes. In order to perform structure analysis on the metabolites and to improve sensitivity for the detection of the various surfactants and their metabolites in the environment, the use of various MS-MS techniques has also proven very useful, if not necessary, and in some cases even high-resolution MS is required. 

The LC/MS combination has been practiced for many years. Various types of interfaces have been developed for LC/MS, including the fast atom bombardment (FAB) source by Barber et al. in 1981 and thermospray by Blakely and VestaL in 1983. However, a broad acceptance of... 

The most commonly used FAB interface in LC/MS is known as continuous-flow fast-atom bombardment (CF-FAB) ionization, in which the fast atoms or ions are directed at a target along which the LC eluent flowsd In a CF-FAB, the LC eluent, mixed with a FAB matrix such as 5% aqueous glycerol, is continuously introduced and deposited on the tip of a FAB probe. The maximum flow rate is in the range of 5 to 15 pL/min. A comprehensive review of the principles and application of CF-FAB for LC/MS has been written by Caprioli. ... 

Most of the direct and indirect (transport) interfaces described here use chemical ionization (c.i.) ion-sources, which are not well suited to such polar, non-volatile compounds as tri- and higher oligosaccharides. The thermospray interface, which can operate on an ion-evaporative mode, is capable of producing intact molecular ions from such nonvolatile, polar molecules and should be useful in oligosaccharide analysis. Molecules of this type, however, can also be easily analyzed by fast-atom-bombardment ionization, and use of this technique, coupled to direct liquid introduction and moving-belt interfaces, has been reported. The latter system has been applied to complex oligosaccharide analysis. ... 

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