F.a.b.-Mass Spectra

Consequently, the only pseudomolecular ions produced are [M+Na] species. These are usually abundant, permitting the observation of molecular ions up to at least 6000. 

spectra are characterized by (a) abundant, pseudomolecular ions for both the sample and the matrix, and (b) a relatively high level of chemical noise, resulting in a signal at every mass number up to the 

Pseudomolecular ions do not appear as single, clean signals in f.a.b. spectra. Instead, clusters of signals are always present, partly because of the presence of molecules containing the C isotope, the natural abundance of which is 1.1%, and partly because oxidations and reductions can occur in the matrix during the f.a.b. experiment. For example, underivatized 

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IV. Interpretation of F.a.b.-Mass Spectra 1. Molecular-weight Assignment... 

The compositions of high-mannose oligosaccharides isolated from urine of animals suffering from genetic or chemically induced mannosidoses have been assigned from their f.a.b.-mass spectra. After chromatography, some samples were sufficiently pure to be examined underivatized. Others required conversion into their peracetylated derivatives. 

The F.A.B. mass spectra results (Table 1) demonstrate the mononuclear di-imine nature of all but one of the products. The exception... 

Figure 6.13 (a) Total ion current chromatogram of the extract of the irradiated TNT solution, (b) Mass spectra of peaks a, d and f, as extracted from this chromatogram. Reprinted with permission from Godejohann, M., Astratov, M., Preiss, A., Levson, K. and Miigge, C., Anal Chem., 70, 4104-4110 (1998). Copyright (1998) American Chemical Society... 

Figure 11.6 Positive ion electrospray mass spectra of an equimolar mixture of five standard proteins, under different instrumental settings, showing cases where prominent signals for the different charge states of (A) insulin, (B) ubiquitin, (C) cytochrome c, (D) lysozyme, and (E) myoglobin were preferentially observed, and (F) where signals for all the proteins were more uniformly detected.

Figure 21.7 Comparison of mass spectra obtained from rat brain. Optical observation of microspotted tissue sections employing spray-droplet (a), droplet (b), and spraycoating (c) methods. Scale bar, 1.0 mm. White squares (a-c) represent the cortex (A, d) and the medulla (B, e) of the cerebellum region, respectively. Accumulated mass spectra collected from each region are shown (d, e). In each spectrum, asterisks represent major unique signals for spectra using the spray-droplet method. The number of detected signals in the mass range of 2000 < m/z < 30,000 from each region is shown (f). Reprinted with permission from Sugiura et al.7...

Figure 8.8 Mass spectra of (a) betulin (TMS derivative), (b) lupeol (TMS derivative), (c) lupa 2,20(29) dien 28 ol (TMS derivative), (d) betulone (TMS derivative), (e) lupenone and (f) lupa 2,20(29) diene...

Figure 8.14 Mass spectra of 15 hydroxy 7 oxo dehydroabietic acid after (a) methylation, (b) methylation followed by trimcthylsilylation and (c) trimcthylsilylation. Reproduced from K. J. van den Berg, J. J. Boon, I. Pastorova, L. F. M. Spetter, J. Mass Spectrom., 35, 512 533. Copyright 2000, with permission from John Wiley Sons, Ltd...

Fig. 2.9.7. (a) ESI-FIA-MS(+) and (b) APCI-FIA-MS(+) overview spectra of synthetically produced mixture of di-carboxylated PEG homologues (f) APCI-LC-MS(+) and (j) APCI-LC-MS(-) RICs of mixture as in (a,b) (c-e) selected mass traces of di-carboxylated PEG homologues under positive and (g-i) negative ionisation. Gradient elution separated by RP-Ci8 column [24]. 

Fig. 1.2 El mass spectra of derivatized phenylalanine, isolated from 5. obliquus a unlabeled, b random 50% 2H-, c random 70% 2H-, d 100% 2H-, e 3C, 5N-, and f 13C, 5N/random 75% 2H-labeled.

McLafferty, F.W. Stauffer, D.B. Twiss-Brooks, A.B. Loh, S.Y. An Enlarged Data Base of Electron-Ionization Mass Spectra. J. Am. Soc. Mass Spectrom. 1991, 2, 432-437. 

As discussed in Sections II,B and C, the 4-oxo-4//-pyrido[l,2- ]pyrimi-dines have often been incorrectly described as 2-oxo-2/f-pyrido[l,2-a]-pyrimidines34-38-92 or as 1,8-naphthyridines.33-81128 These three types of compounds can be distinguished on the basis of their UV, NMR, and mass spectra. 

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