Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume
38, Number 8, August 2000, pp. 357-364
The
Use of Linear Expressions of Solute Boiling Point Versus Retention to Indicate
Special Interactions with the Molecular Rings of Modified Cyclodextrin Phases
in Gas ChromatographyT.J.
Betts
School of Pharmacy, Curtin University of Technology, GPO Box U1987, Perth 6845,
Western Australia, Australia
The boiling
points (°C, 1 x 10) of diverse C10 polar solutes from volatile oils are
set against their relative retention times versus n-undecane to calculate linear
equations for 12 commercial modified cyclodextrin (CD) capillary phases. Ten
data points are considered for each CD, then solutes are rejected until 5 or
more remain that give an expression with a correlation coefficient of at least
0.990 and a standard deviation of less than 5.5. Three phases give almost perfect
correlation, and 3 other CDs have difficulty complying. Solutes involved in
the equations (most frequently cuminal, linalol, and carvone) are presumed to
have a standard polar transient interaction with the molecular rings
of the CDs concerned. Several remaining solutes (mostly citral, fenchone, and
menthol) exhibit extra retention over the calculated standard (up to 772%),
which is believed to indicate a firm host CD or guest
solute molecular fit in some cases. Other solutes show less retention than calculated
(mostly citronellal, citronellol, estragole, and pulegone). This suggests rejection
by the CD, which behaves merely as a conventional stationary phase to them.
The intercept constant in the equation for each phase is suggested to be a numerical
relative polarity indicator. These b values indicate that 3 hydroxypropyl CDs
show the most polarity with values from 28 to 43; and CDs that are fully substituted
with inert groups fall in the range of 15 to 20.
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