The hydrocarbons of Recent Polluted.., sediments, in-reservoir and laboratory
biodegraded crude oils, and certain petroleum products (e. g. lubricating oils)
often display "humps" or Unresolved Complex Hixtures (UCHs) when analysed by
gas chromatography (CC). Although widespread and often abundant, to date
little is known of their detailed molecular composition.
Standard chromatographic methods of isolation of model aliphatic and aromatic
hydrocarbon UCMs from lubricating oils followed by conventional methods of
analysis provided little compositional detail. Thus CC and CC-electron impact
mass spectrometry (GC-EIMS) was limited to an estimate of carbon number
ranges and to the identification of certain series of *biological marker"
compounds. However, these were well resolved and were estimated to account
for <10% of the total detector response. Further analyses were performed by
chemical ionisation-MS (CI-MS), probe distillation EI-MS, field ionisation-MS
(FIMS), and elemental analysis; yet the information provided by each was
limited to a few "average, molecular types.
In view of the limitations of conventional methods of analysis, alternative
methods were adopted. These utilised novel chemical and pyrolytic degradations
of the UCM hydrocarbons. Chemical oxidation with Cr03 in glacial acetic acid
produced reasonable yields of total recoverable material (40-80%).
Furthermore, a high proportion were functionalised (>90%), and many resolved,
which allowed their identification by EI and CI GC-MS.
Surprisingly, the most abundant products of oxidation of hydrocarbon UCMs were
straight chain monocarboxylic acids. This appeared to contradict literature
consensus on UCM composition, namely a predominance of highly branched and/or
cyclic hydrocarbons. However, from literature reported CrO oxidations of
hydrocarbons, potential precursor compounds were proposel. These were
monoalkyl substituted "TO-branched acyclic and monocyclic. alkanes for the
aliphatic UCM and alkyl "TO-branched monoaromatic hydrocarbons for the
aromatic UCM.
Proposed precursor UCM hydrocarbons were confirmed by synthesis and chemical
oxidation under the same conditions. Thus each of the synthetic candidate UCM
hydrocarbons [7-n-hexylnonadecane, 9-(2-phenylethyl)-heptadecane. and 9-(2-
cyc 1 ohexyl ethyl j--hep tade cane ] produced n-acids on oxidation with Cr03-
Further correlations were found for producits of other synthetic alkanes and
less abundant UCM oxidation products. For example, n-alkan-2-ones. iso alkan-2-
ones, and 7-methyl--y-lactones could all be correlated with methyl substituted
acyclic alkyl linkages on UCM hydrocarbons.
The application of chemical oxidation to aliphatic UCMS of varied origin
showed the technique has great potential for ofingerprintingm such samples.
GC-MS analysis of a selected series of resolved product compounds (alkyl
ketones, -y-methyl--y-lactones) showed good correlations for samples of the sane
origin, yet distinct differences for UCHs from different sources.
Biodegradation of the three candidate UCM hydrocarbons alongside acyclic
isoprenoid alkanes and normal and monomethyl alkanea showed the UCM
hydrocarbons were at least as resistant to microbial degradation as the
isoprenoid alkanes. In this context it is therefore concluded that the
candidate UCM compounds serve as good molecular models for hydrocarbon UCMs.
Date of Award | 1989 |
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Original language | English |
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Awarding Institution | |
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- Water Pollution
- Sewage Chemistry
- Organic Water Pollution
- Hydrocarbon pollution
Characterisation of unresolved complex mixtures of hydrocarbons
Gough, M. A. (Author). 1989
Student thesis: PhD