Matrix, for FAB

B. J. Sweetman and I. A. Blair. 3-Nitrobenzyl Alcohol Has Wide Applicability as a Matrix for FAB-MS. Biomed. Environmental Mass Spectrom., 17(1988) 337-340. 

Musselman, B. Watson, J.T. Chang, C.K. Direct Evidence for Preformed Ions of Porphyrins in die Solvent Matrix for FAB-MS. Org. Mass Spectrom. 1986, 27, 215-219. 

The choice of matrix for FAB-MS, LSIMS, and MALDI is essential for efficient sample ionization. For example, the use of 3-nitroben-zyl alcohol instead of glycerol, thioglycerol, or most other more common matrices is essential for the formation of abundant carotenoid ions during FAB and LSIMS. Nonpolar carotenoids (e.g., the carotenes) are insoluble in polar ma-... 

The quest for an ionization method that guarantees a molecular ion for all compounds has driven the development of softer and softer methods. As the goal is approached, a wealth of new exceptions to the rule have been observed. Cluster ions and adduct ions form in the matrix (for FAB ionization) or in the spray of the API methods, depending on the nature of the compound, the matrix, the solvent, or extraneous salts present in the sample or in the instru-... 

Mass spectral analyses were carried out on a JEOL DX-303. Glycerol was used as the matrix for FAB-MS analysis. 

Sample preparation for FAB is primarily dissolving the analyte in a liquid matrix. The matrix plays... 

Quantitative analysis using FAB is not straightforward, as with all ionisation techniques that use a direct insertion probe. While the goal of the exercise is to determine the bulk concentration of the analyte in the FAB matrix, FAB is instead measuring the concentration of the analyte in the surface of the matrix. The analyte surface concentration is not only a function of bulk analyte concentration, but is also affected by such factors as temperature, pressure, ionic strength, pH, FAB matrix, and sample matrix. With FAB and FTB/LSIMS the sample signal often dies away when the matrix, rather than the sample, is consumed therefore, one cannot be sure that the ion signal obtained represents the entire sample. External standard FAB quantitation methods are of questionable accuracy, and even simple internal standard methods can be trusted only where the analyte is found in a well-controlled sample matrix or is separated from its sample matrix prior to FAB analysis. Therefore, labelled internal standards and isotope dilution methods have become the norm for FAB quantitation. 

For FAB/LSIMS, the analyte should be soluble to at least 0.1 mgml in some solvent or even better directly in the matrix concentrations of 0.1-3 [jg piP in the matrix are ideal. In case of extremely low solubility, additives such as other solvents, acids or surfactants can help. [74]... 

General. NMR spectra were obtained on a Bruker WM-250 instrument with tetramethylsilane (TMS) as internal standard. UV-visible spectra were taken on a Varian Cary 219. Fast-atom bombardment (FAB) mass spectrometry (MS) analysis were completed on a Vacuum Generators ZAB-2F double-focusing or a Varian MAT CH5 mass spectrometer equipped with an Ion Tech FAB Gun. Solvents for FAB matrix were made up of thioglycerol, dithiothreitol, and dithioerythretol (2 1 1) addition of 0.1M trifluoroacetic acid to the matrix facilitated the ionization of the porphyrins during FAB analysis.(13)... 

FAB peptide preparation is accomplished by dissolving a relatively pure (>70%) peptide sample into a 3-nitrobenzyl alcohol (NBA) matrix. There are many matrices used in FAB analyses, however, 3-nitrobenzyl alcohol has become a standard for FAB peptide analysis (Figure 12). The peaks associated with the NBA matrix can make the spectra more cumbersome to interpret. However, to the experienced mass spectroscopist the matrix ions can act as reference ions and are a useful indicator of accuracy. Rarely are the NBA matrix ions observed above m/z 1000. 

FIGURE 2.5. Schematic for FAB mass spectrometry. The intense activity at the surface of the sample produces neutrals, sample ions, ions from the matrix, etc. Only the ions are accelerated toward the analyzer. 

In widespread use since 1982 (Barber et al., 1982), FAB and LSIMS are matrix-mediated techniques. The most effective matrix for static FAB/LSIMS analysis of chlorophylls and their derivatives is 3-nitrobenzyl alcohol (van Bree-men et al., 1991a), whereas glycerol provides adequate sensitivity and a more robust system during continuous-flow FAB/LSIMS (van Breemen et al., 1991b). Ionization and desorption of the chlorophyll analyte occur together during the bombardment of the matrix by fast atoms (or ions) to produce molecular ions, M+-, and protonated molecules, [M+H]+. 

Matrix Considerations Non-volatile and thermally fragile molecular samples are dissolved in a liquid matrix for introduction into the spectrometer to perform FABMS measurements. The properties generally Imposed upon the matrix include ability to dissolve samples and possession of low vapor pressure to extend life time in the vacuum environment. Sample life time should be several minutes to be able to optimize the spectral signal and make several spectral runs. Many organic liquids that satisfy these requirements have been used to obtain FAB data by several investigators (7, 31, 32). Two of the more often used matrices are glycerol and thioglycerol In addition, a liquid metal matrix was used to float the sample to obtain FABMS spectra (33). 

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