I. Spanik et al., Comparison of two methods for the gas chromatographic determination of thermodynamic parameters of enantioselectivity, J CHROMAT A, 843(1-2), 1999, pp. 123-128
The thermodynamic parameters responsible for the formation of diastereomeri
c associates between enantiomers of methyl lactate and two Lipodex E column
s [with 5.37% or 10.08% of octakis(3-O-butanoyl-2,6-di-O-pentyl)-gamma- in
SE 54] were calculated using two different methods. Method A was based on t
he direct determination of Delta(Delta G(R,S)(0)) from experimental values
of the chiral separation factor a obtained at different temperatures for th
e separation of the enantiomers of methyl lactate on two Lipodex E columns.
Method B relies on the determination of the relative retention of the enan
tiomers of methyl lactate in respect to an inert reference standard on a re
ference column containing only the solvent and that of the enantiomers of m
ethyl lactate to the same reference standard on the reactor column containi
ng the cyclodextrin derivative in the solvent S. SE 54 was used as solvent
for Lipodex E and n-heptane, n-octane and n-nonane were used as reference s
tandards. Obtained results for Delta(R,S)(Delta G(0)) show that the data ca
lculated by Method A are too small and are dependent on the concentration o
f the chiral selector in the diluted stationary phase. Since the dependence
of In alpha on 1/T for methyl lactate enantiomers on Lipodex E columns was
nonlinear, it was not possible to calculate Delta(R,S)(Delta H-0) and Delt
a(R,S)(Delta S degrees) values by this method. Results obtained by Method B
are essentially independent on the choice of reference compound and the co
ncentration of the chiral selector in the mixed stationary phase. (C) 1999
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