Mass spectral interpretation significance

The GC separations, derivatization procedures, mass spectral interpretation, structure correlations, and other information presented in this book were collected or experimentally produced over the length of a 30-year career (F.G.K.) in GC/MS. It has not been possible to reference all sources therefore, in the acknowledgments, we thank those persons whose work has significantly influenced this publication. 

A full-scan mass spectrum can easily be obtained from this amount of material and it should be clear, therefore, that even high-pnrity (and nsually expensive ) solvents can give rise to a significant mass spectral backgronnd, hence rendering the interpretation of both qnalitative and qnantitative data difficult. 

In the intervening 13 years the subject has expanded dramatically over 60 compounds are now classified as Erythrina alkaloids, and the structures of most of these have been deduced from a combination of mass spectral fragmentation analysis, H-NMR spectral interpretations, and chemical correlations with alkaloids of known structures. Some unusual alkaloids have been obtained from certain Cocculus species and a new, as yet small, subgroup, the Homoerythrina alkaloids, has been recognized. The biosynthetic pathway from tyrosine through the aromatic bases to the ery-throidines has been elucidated, and some significant advances have been made in methods of total synthesis. Reviews of the Erythrina alkaloids since 1966 have appeared (3-6). 

Thus the next step in the interpretation of the spectrum is to note the possible structural significance of all important peaks. Where more than one possible interpretation exists, be sure to note all of them if other evidenee in the spectrum eliminates one or more of these possibilities, these remaining will be much more meaningful. Possible assignments for ions are given as part of the ion series of Table A.6. Mass Spectral Correlations (McLafferty and Venkataraghavan... 

FAB-MS Profile. As with the lysophosphatidic acids, this type of mass spectrometry can be useful in establishing the structural characteristics of PAs in a mixture. Interpretation of the spectral patterns is slightly more complex than for the lysophosphatidic acids due to the presence of additional fatty acyl residues. Nevertheless, a subtractive approach as described for the lysophosphatidic acids can be of significant help. Even with the complexities encountered in a sample, the FAB-MS methodology is a potent aid in elucidating the structure of these compounds. 

NMR spectral analysis did not yield a definitive answer because of complications caused by limited sample mass, contaminants present in the sample, and most significantly, a rotamer effect arising from two separate amides. This gave rise to very complex NMR spectra that were not easily interpreted. In this study, the structure of the impurity was based on the LC/MS/MS data only. 

No attempt will be made here to review and correlate the large number of ultraviolet, infrared, nuclear magnetic resonance, and mass spectra that have been recorded, interpreted, and used in structure determination of pyridinols and pyridones. Articles that contain significant spectral data and/or discussions are noted in the Tables. The role of spectroscopic techniques, ionization constants, and dipole moments in the studies of structure and tautomerism of heterocyclic compounds has been reviewed recently by Albert. Although ionization constants have been used to estimate pyridinol-pyridpne equilibrium constants with some success, caution must be exercised about drawing conclusions from this type of data. ... 

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