Fast atom bombardment mass advantages

Lattimer and co-workers [25] have applied mass spectrometry (MS) to the determination of antioxidants and antiozonants in rubber vulcanisates. Direct thermal desorption was used with three different ionisation methods [electron impact (El), chemical ionisation (Cl), field ionisation (FI)]. The vulcanisates were also examined by direct fast atom bombardment mass spectrometry (FAB-MS) as a means for surface desorption/ionisation. Rubber extracts were examined directly by these four ionisation methods. Of the various vaporisation/ionisation methods, it appears that field ionisation is the most efficient for identifying organic additives in the rubber vulcanisates. Other ionisation methods may be required, however, for detection of specific types of additives. There was no clear advantage for direct analysis as compared to extract analysis. Antiozonants examined include aromatic amines and a hindered bisphenol. These compounds could be identified quite readily by either extraction or direct analysis and by use of any vaporisation/ionisation method. 

If high-resolution measurements are performed in order to assign elemental compositions, internal mass calibration is almost always required. The calibration compound can be introduced from a second inlet system or be mixed with the analyte before the analysis. Mixing calibration compounds with the analyte requires some operational skills in order not to suppress the analyte by the reference or vice versa. Therefore, a separate inlet to introduce the calibration compound is advantageous. This can be achieved by introducing volatile standards such as PFK from a reference inlet system in electron ionization, by use of a dual-target probe in fast atom bombardment, or by use of a second sprayer in electrospray ionization. 

There are several types of ionization sources [MALDI, ESI, FAB (fast atom bombardment), PD (Cf-252 plasma desorption), El (electron ionization), Cl (chemical ionization) etc.], different types of mass analyzers [combinations of magnetic and electric sectors, quadrupolar filters (Q) and ion traps (IT), time-of-flight (TOF) and FT-ICR] and different detectors, each with its own advantages and drawbacks. We describe herein only the systems that presently have widespread use for the study of biomolecules ESI coupled to a quadrupole (or triple quadrupole, QqQ) mass analyzer or an ion trap, the MALDI source with the linear or reflectron TOF analyzer, and the FT-ICR system which can be equipped with both ESI and MALDI sources. 

Recent advances in mass spectrometry have produced a number of soft ionisation techniques such as fast atom bombardment (FAB) or electrospray ionisation. The major advantage of these techniques is that they are less likely to break the sample into small fragments and are more likely to produce a molecular ion. This is particularly important in the analysis of macromolecules such as proteins and nucleic acids. 

One of the most powerful techniques used in Upid analysis today is HPLC coupled with mass spectrometry (HPLC/MS). Several mass spectrometric ionization techniques, such as fast atom bombardment (FAB) [23], electrospray ionization (ESI) [29,30], ionspray ionization (ISI) [31], and atmospheric pressure chemical ionization (APCI) [22,30,32] have been used. By using HPLC/MS, one can get information on the molecular structure of the intact lipids, which helps differentiate molecular species within different lipid classes. By using tandem mass spectrometry (MS/MS), identification of molecular species of different sphingolipids can be achieved in an easier and more sensitive way. There are many other advantages of using MS, such as small sample size, minimal sample preparation, and lack of need for derivatization, speeds, and sensitivity. In the literature, sphingolipids of both animal and plant origin were analyzed by MS. 

Soft ionization MS techniques [9] like electrospray ionization (ESI) and soft laser desorption, often known as matrix-assisted laser desorption/ioniza-tion (MALDI), facilitated the polymer analyses over the last years. The advantage of the soft ionization techniques is the transformation of dissolved liquid or solid sample into the gas phase, where no change in the molecular composition/structure of the sample will be induced, while hard ionization in mass spectrometry (e.g., electron ionization (El) or fast atom bombardment (FAB)) preferentially destroys the chemical and molecular structure into fragments prior to the detection of the molar mass fragments of the sample by mass spectrometry. 

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. 

One of the major problems in analytical chemistry is the detection and identification of non-volatile compounds at low concentration levels. Mass spectrometry is widely used in the analysis of such compounds, providing an exact mass, and hence species identification. However, successful and unequivocal identification, and quantitative detection, relies on volatilization of the compound into the gas phase prior to injection into the analyser. This constimtes a major problem for thermally labile samples, as they rapidly decompose upon heating. In order to circumvent this difficulty, a wide range of techniques have been developed and applied to the analysis of nonvolatile species, including fast atom bombardment (FAB), field desorption (FD), laser desorption (LD), plasma desorption mass spectrometry (PDMS) and secondary-ion mass spectrometry (SIMS). Separating the steps of desorption and ionization can provide an important advantage, as it allows both processes to be... 

Several mass spectrometric techniques including fast atom bombardment (FAB), plasma desorption (PD), matrix-assisted laser desorption/ionization (MALDI), and electrospray (ES) mass spectrometry (MS) are presently available for the analysis of peptides and proteins (Roepstorff and Richter, 1992). Of these techniques, mainly PDMS has gained footing in protein laboratories because the instrumentation is relatively cheap and simple to operate and because, taking advantage of a nitrocellulose matrix, it is compatible with most procedures in protein chemistry (Cotter, 1988 Roepstorff, 1989). Provided that the proper care is taken in the sample preparation procedure most peptides and small proteins (up to 10 kDa) are on a routine basis amenable to analysis by PDMS. Molecular mass information can be obtained with an accuracy of 0.1% or better. Structural information can be gained by application of successive biochemical or chemical procedures to the sample. 

For the HPLC-MS systems, many different ionization techniques have been described in the past. Various interface, ionization methods, and operating techniques applicable to LC-MS are discussed in [117J for instance Thermospray, particle beam, electrospray (ES), field desorption (FD), fast atom bombardment (FAB), time of flight (TOF), etc. The electrospray technique produces a soft ionization for thermally labile compounds, while FAB has the advantage that higher molecular mass samples can be introduced into the mass spectrometer. Table 8 offers a rough guide to the applicability of various LC-MS interfaces. For more detailed information on LC-MS, see [118]. 

Procedures for etherification and esterification of carbohydrates for GLC analysis, advantages and disadvantages of the different methods of hydroxyl and aldehyde group derivatization, columns used for the separation of the various derivatives, detection methods for GLC, mass spectroscopy and fast atom bombardment (FAB) as well as outlines of some strategies for structural analysis of carbohydrates are described, discussed and reviewed in an excellent book on the analyses of carbohydrates by GLC (35). 

Fast atom bombardment (FAB) mass spectrometry was developed in the 1980s and has a number of advantages over FI molecular masses up to 10 000 can be determined, the instrument can be run in both positive and negative modes permitting both positive and negative ions to be... 

Carnitine and its esters (see [1]) cannot be introduced to the mass spectrometer by gas chromatography, as they incorporate quaternary amine functions and will decompose in the attempt. Fast atom bombardment (FAB) and electrospray ionization (ESI) can use the formal charge on the quaternary amine function to advantage, as carnitine and its esters are very easily desorbed from glycerol on the FAB probe and from aerosol sprays in ESI. Eigure 7A illustrates the use of EAB in the quantitation of carnitine and its esters excreted in the urine of a patient presenting with a severe dicarboxylic aciduria associated with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. 

A modification of the FAB technique is continuous flow FAB (CFFAB). In this approach, the sample in solution is introduced into the mass spectrometer through a fused silica capillary. The tip of the capillary is the target. The solution is bombarded by fast atoms produced as described earlier. Solvent is flowing continuously and the liquid sample is introduced by continuous flow injection (Fig. 9.13). The mass spectrum produced has the same characteristics as that from conventional FAB, but with low background. Typically, the solvent used is 95% water and 5% glycerol. The ability to inject aqueous samples is an enormous advantage in biological and environmental studies. 

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