THEORETICAL APPROACH TO THE GAS-CHROMATOGRAPHIC SEPARATION OF ENANTIOMERS ON DISSOLVED CYCLODEXTRIN DERIVATIVES

The theoretical concept described previously for enantiomer separation by complexation gas chromatography was extended to polysiloxane stationary phases containing dissolved cyclodextrin derivatives. A relationship between the chiral separation factor-alpha and the cyclodextrin molality was derived. The theory was verified by comparing the predicted and measured dependence of alpha on the cyclodextrin molality for various racemates. Retention increases R' were determined as a measure of the enantiomer-cyclodextrin interactions and of the contribution of these interactions to the total retention time. By measuring R' at different temperatures, Gibbs-Helmholtz parameters (DELTA-R,S-DELTA-G, DELTA-R,S-DELTA-H and DELTA-R,S-DELTA-S) of enantiomer discrimination were obtained from the ln (R'R/R'S) vs. 1/T plots. Because of the difficulty of finding a truly inert reference standard, these data are affected by a systematic error which restricts the interpretation of the observed enantioselectivities to a qualitative manner.