Sorption and enantioselective properties of binary stationary phases based on polydimethylsiloxane and polyethyleneglycol and additive of heptakis-(2,3-Odiacetyl- 6-O-tosyl)-β-cyclodextrin under gas chromatography conditions

Abstract

The subject of the study were two binary polymer systems – non-polar (polydimethylsiloxane PMS,
Mr=5000) and polar (polyethyleneglycol, PEG, Mr=400) with the addition of (10 wt.%) of first synthesized
bifunctional derivative of β-cyclodextrin – heptakis-(2,3-O-diacetyl-6-O-tosyl)-β-cyclodextrin (Ac-Tz-β-
CD). The aim of the work was to study the thermodynamic characteristics of sorption and complexation of
the type of "guest - host" for volatile organic compounds in the columns with binary stationary phases based
on polymers (PMS, PEG) and chiral additive (Ac-Tz- β-CD).
Method of inverse gas chromatography was used to determine the specific retention volumes for 29
organic compounds of different classes, including optically active; for columns with binary fixed source
"pure" polymers enthalpy and entropy contributions to the retention and thermodynamic characteristics of
complex formation were calculated.
It was established that in the system "PMS - Ac-Tz-β-CD" complexation of the "guest - host" type is
weak, with the exception of polar compounds with a small molecular volume. This phase has a high
enantioselectivity in relation to the optical isomers of menthol in a wide temperature range. For a large number of investigated non-polar and polar sorbates in the system "PEG - Ac-Tz-β-CD" complexation with
exothermic heat effect was observed. This system has a moderate enantioselectivity towards terpene
hydrocarbons.
The results of the work are important for the development of supramolecular chemistry of polymeric
systems, and the development and manufacture of capillary separation columns of type WCOT for chiral gas
chromatography. For the first time a bifunctional derivative β-cyclodextrin - heptakis-(2,3-O-diacetyl-6-Otosyl)-
β-cyclodextrin was used as a component of mixed polymeric sorbent for gas-liquid chromatography. It
is shown that the nature of the sorbent polymer matrix affects the ability of complexing with dissolved
organic compounds Ac-Tz-β-CD. With use of polyethyleneglycol - 400 complexing effect was observed for
more organic compounds than with polydimethylsiloxane. Polydimethylsiloxane-based sorbent showed
higher enantioselective properties relative to the isomers of menthol, while the sorbent on the
polyethyleneglycol basis showed enantioselective properties with respect to the optical isomers of limonene
and camphene