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Mass spectrometry and gas chromatography in chemical analysis and identification : experimental factors and case studies

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Davies, Noel William (1993) Mass spectrometry and gas chromatography in chemical analysis and identification : experimental factors and case studies. PhD thesis, University of Tasmania.

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Abstract

This thesis is based on developments in mass spectrometry
(MS), gas chromatography (GC) and combined gas
chromatography-mass spectrometry (GC-MS) as analytical
techniques, and specific applications of these
developments and traditional MS and GC-MS to the analysis
of organic samples. The majority of this work has been
published in the refereed scientific literature.
A detailed theoretical study was undertaken into the
relationships between chromatographic resolution in
combined GC-MS and carrier gas flow rate. The influence
that the type of GC-MS interface has on optimum flow rate
requirements was quantified. A simple equation relating
column length, column 'hold-up' time and volumetric flow
rates in directly coupled capillary GC-MS was derived,
facilitating the setting of the appropriate optimum gas
flow in this mode.
Average linear gas velocities and flow rates required to
deliver optimum performance for a variety of column
diameters, carrier gases and types of GC-MS interface
were reported, together with the 'hold-up' times and
inlet pressures necessary to deliver these values. The
dependence between carrier gas flow rates, average linear
velocities and temperature programming was determined for
a number of GC-MS interface and flow control
combinations. Discrimination caused by the 'open-split'
interface in GC-MS was examined, and a numerical
relationship was established between GC oven temperature
and effluent yield in temperature programmed analyses.
A GC-MS screening procedure for a large group of target
analytes was created using a 'bench-top' quadrupole mass
spectrometer, enabling automatic detection at trace
levels of genuine or potential 'positives' from crude
extracts. Two representative ions of the target substance
had to occur in the correct ratio and at a specific and
automatically adjusted retention time for a 'positive'
report. For maximum sensitivity a number of time windows
were created, and selected ion monitoring of the two
characteristic ions for each target compound was carried
out. Although the protocol was developed for screening
extracts of biological fluids for drugs, it could be
applied to screening for target compounds from any
matrix.
The technique of 'Selected Reaction Monitoring' of
fragmentations within the first field-free region of a
double-focussing instrument of Nier-Johnson geometry was
developed, and applied to the quantitative determination of drugs and drug metabolites from body fluid extracts
using stable isotope labelled internal standards. This
method, an aspect of the now widely adopted 'Mass
Spectrometry/Mass Spectrometry' (MS/MS) techniques,
greatly increased the specificity of the detection of
target compounds. Warfarin from human blood and N-hydroxy
phenacetin from human urine were quantified by this
technique. These two examples were among the first to use
a conventional geometry mass spectrometer in this way for
the simultaneous monitoring of daughter ions from
different parents from the first field-free region of the
spectrometer.
Conventional low and high resolution MS and GC-MS were
applied to the analysis of essential oils, wasp
secretions and plant gums and waxes. The essential oils
of six hop cultivars were analysed in detail,
particularly with respect to the levels of selinene
isomers. Commercial extracts of Boronia megastigma
flowers were analysed by GC-MS; (Z)-heptadec-8-ene and
dodecyl acetate were identified as major components,
together with the new oxygenated sesquiterpene
'sesquicineole' in some clones, and some fifty other
volatile components.
A library of several hundred reference mass spectra was
compiled to enable analyses on a range of essential oils
to be undertaken. This was made available to the MS
community via the U.S. National Institutes of Standards
and Technology (NIST) database. A collection of 'Kovats'
GC retention indices, important corroborative evidence
for the MS identification of essential oil related
compounds, was obtained from a diverse range of
literature sources for 400 mono- and sesquiterpenes. This
collection of data was published as a review article. Based on MS evidence in conjunction with microchemical
reactions and subsequent comparison with authentic
standards, (E,E)-2,8-dimethy1-1,7-dioxaspiro[5.5]-
undecane, (E,E)-2-ethy1-7-methy1-1,6-dioxaspiro[4.5]-
decane, (Z,E)-2,8-dimethy1-1,7-dioxaspiro[5.5]undecane
and 2-methyl-6-penty1-3,4-dihydro-2H-pyran were
identified in the mandibular gland secretions of
parasitic wasps. The structures of three new
cycloartenone related triterpenes from Gardenia species
were determined primarily by MS from first principles;
these were 9,19-cyclolanostan-3,24-dione, 9,19-
cyclolanost-24-en-3,23-dione, and 9,19-cyclolanostan-
3,23-dione.

Item Type: Thesis (PhD)
Keywords: Organic compounds, Mass spectrometry, Gas chromatography
Copyright Holders: The Author
Copyright Information:

Copyright 1993 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1994. Includes bibliographical references

Date Deposited: 08 Dec 2014 23:57
Last Modified: 09 May 2016 06:23
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