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APPLICATIONS OF MASS SPECTROMETRY IN BIOLOGICAL, ENVIRONMENTAL AND GAS-PHASE ORGANIC ION CHEMISTRY
Abstract
Part I. In this thesis we describe an application of high performance mass spectrometry to the structural determination of a complex biological molecule-the ornithine-containing lipid from Thiobacillus Thiooxidans. The mass spectral techniques of metastable scanning, high resolution and chemical ionization have been applied to this determination and some aspects of these techniques will be presented as background. These methods are applied to generate the fragmentation pathways occurring in the electron impact decomposition of the ornithine lipid. The spectrum of the ornithine-containing lipid did not contain a molecular ion for the intact lipid but was consistent with cyclization of the ornithine zwitterionic moiety with elimination of water to give 3{3'-(11,12-methylene-2-hydroxyoctadecanoxy)hexadecanylamine-2-piperidone}. The spectrum can be understood to arise by three primary decompositions which serve to separate the two fatty acid constituents. The remainder of the spectrum is consistent with the expected fragmentation of these constituents. To investigate further the thermolysis, we have studied the methane, isobutane and ammonia chemical ionization spectra. The results show that thermolysis occurs in at least two steps. Dehydration of the ornithine produces a substituted piperidone and this fragment undergoes a facile elimination to produce a long chain fatty acid and piperidone-containing fatty amide. In the course of this work, we have discovered a new interference which can occur in the V(' 1/2)/E linked defocussed metastable scanning method. This interference is described and equations are given to explain its occurrence in a metastable spectrum. We describe a second widely accepted application of high resolution mass spectrometry: trace analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin. This substance has become the subject of numerous analytical studies in recent years because of its extreme toxicity and the consequences of its presence in the environment. A high resolution mass spectrometer/signal averager system was developed and employed for analyzing 2,3,7,8-tetrachlorodibenzo-p-dioxin at the parts-per-trillion level. An ultimate detection limit of 50 femtograms is demonstrated. Part II. In this section of the thesis, we present a study extending our understanding of how energy is partitioned in unimolecular decompositions. A summary of the current theory is presented first and includes an explanation of kinetic energy release, a key parameter in understanding energy partitioning. In this study we have generated the energy partitioning quotient for loss of water from the molecular ion of o-methylbenzyl alcohol and various derivatives. From the data, we conclude that the large kinetic energy release observed for loss of water from the alcohol is an indication of a larger fraction of energy partitioned into the translational mode for this compound than for the other members of the series. The occurrence of this larger fraction is surprising in light of the fact that the mechanism for loss of water from the molecular ion of each of the compounds is a proven 1,4-elimination. Since current theory states that the fraction of energy partitioned is directly proportional to the entropy of activation, the apparent contradiction is discussed.
Subject Area
Analytical chemistry
Recommended Citation
HILKER, DAVID RICHARD, "APPLICATIONS OF MASS SPECTROMETRY IN BIOLOGICAL, ENVIRONMENTAL AND GAS-PHASE ORGANIC ION CHEMISTRY" (1981). ETD collection for University of Nebraska-Lincoln. AAI8110572.
https://digitalcommons.unl.edu/dissertations/AAI8110572