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|Title: ||Selectivity and applications of supercritical fluid chromatography|
|Authors: ||Sanagi, M. Marsin|
|Issue Date: ||1988|
|Publisher: ||© M.M. Sanagi|
|Abstract: ||Supercritical fluid chromatography (SFC) has been undergoing
tremendous developments in recent years as an attractive technique that
is complementary to both gas and liquid chromatography. The main aim of
this study has been to examine selectivity in SFC by using retention
indices as the means of recording retention and to explore the potential
applications of this novel technique.
A simple supercritical fluid chromatograph was constructed based on
a Pye-Unicam gas chromatograph and a HPLC pump. SFC separations were
carried out using HPIC packed columns with pure or modified carbon
dioxide as the mobile phase and using ultraviolet and flame ionization
detection. The effects of different parameters on the retention of
compounds. of different functional groups have been studied.
At a given temperature, the capacity factors of the compounds
generally decreased with increases in pressure (density). Little change
in selectivity was observed between compounds in a homologous series but
selectivity differences were observed between compounds of different
functionalities and anomalous behaviour was seen for acetophenone on a
cyano-silica column. Temperature can also be used to selectively modify
the retention of the analytes. The use of methanol or acetonitrile as
the organic modifier generally improved the peak shapes and reduced the
retentions, and this was particularly marked for polar compounds.
Similar trends in retentions were observed for PS-DVB, ODS-, and
cyano-silica columns although the compounds were generally more retained
on the PS-DVB column, suggesting that the selectivity was controlled
mainly by the properties and compositions of the mobile phase.
Using different sets of homologues, alkylarylketones, n-alkanes,
and alkylbenzenes, the possibility of the application of retention
indices in SFC was investigated. The use of retention indices have been
shown to have advantages over capacity factors, but unlike HPLC,
retention indices in SFC are much more susceptible to selectivity
changes caused by variations in the operating parameters.
Studies were carried out to demonstrate the viability of SFC for
the separation of several drug groups, barbiturates and benzodiazepines.
With no modifier in the mobile phase, these compounds were highly
retained on the columns, particularly on ODS- and cyano-silica.
Successful separations of the drug compounds were achieved with methanol
or acetonitrile as the modifier in the mobile phase. The application of
the SFC system was extended to the separations of several terpenes and
the leaf essential oil of Cymbopogon martinii (Roxb.) Wats on a PS-DVB
column. The results were compared with those obtained using GC and GC-MS
methods and it was evident that the GC methods gave better resolutions
and sensitivity and would still be the method of choice.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Chemistry)|
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