January 1979

Document Type


Degree Name



Dept. of Chemistry


Oregon Graduate Center


The use of electron impact mass spectrometry for isotopic analysis is an established technique; however, its application to problems involving biologically produced molecules enriched in 13C has been severely limited. This limitation is shown to arise because of data reduction techniques which are, for practical purposes, incapable of dealing with the complex situation of multiple enrichment sites, limited isotope abundance, and complex spectral regions. Two approaches for detailed isotopic analysis of EIMS intensity are presented and illustrated using model data, literature data, and original data from biosynthetically enriched compounds. The first approach which allows for sequential variation of any one parameter is shown to be of value in experimental design through construction of ion cluster contour diagrams which summarize the variation of isotopic distribution, molecular size, and uncertainty in measurement with total isotopic content. The second approach differs in concept from previous methods and is especially promising for application to problems involving multiple sites of enrichment, limited isotopic abundance, and complex spectral regions. The key concept of this approach is that the roots of the polynomials constructed from observed spectral intensities are analytically related to the isotopic content and the isotopic distribution of the ions giving rise to the intensities.





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