Retention on mixed cyclodextrin/polysiloxane stationary phases in capillary GC?Evidence for the interaction of cyclodextrin and polysiloxane

2,3-di-O-methoxymethyl-6-O-tert-butyldimethylsilyl-beta-cyclodextrin, a useful stationary phase for gas chromatographic separation of enantiomers

Heptakis(2,3-di-O-methoxymethyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin (2,3-MOM-6-TBDMS-beta-CD), synthesized by using methoxymethylchloride (MOM-Cl) as derivatization reagent, was used for capillary gas chromatographic separation of enantiomers. The new chiral stationary phase proved to be suitable for the enantiodifferentiation of volatiles from various chemical classes. Compared to the corresponding gamma-CD derivative (2,3-MOM-6-TBDMS-gamma-CD), the spectrum of compounds for which enantiomers could be separated was more limited and the enantioseparation achieved was generally less pronounced. Unusually high separation factors were observed for 2-alkyl esters of short chain acids (C2-C6). Phenomena underlying the enantioseparation of 2-pentyl acetate (alpha: 4.31; 35 degrees C) were investigated by determining thermodynamic parameters. Data show that only one enantiomer is retained significantly on the chiral stationary phase whereas the other one behaves like the hydrocarbons used as references.

Separation of enantiomers by gas chromatography

The separation of enantiomers by gas chromatography is performed on chiral stationary phases (CSPs) via hydrogen bonding, coordination and inclusion. Thus, typical chiral selectors are amino acid derivatives, terpene-derived metal coordination compounds and modified cyclodextrins. In Chirasil-type stationary phases the chiral selector is anchored to a polysiloxane backbone improving gas chromatographic performance. The present review article describes the state-of-the-art, scope and limitations, applications and mechanistic considerations at the advent of the millennium incorporating 16 figures and 168 references.

Approach to the thermodynamics of enantiomer separation by gas chromatography. Enantioselectivity between the chiral inhalation anesthetics enflurane, isoflurane and desflurane and a diluted gamma-cyclodextrin derivative

The thermodynamics of enantioselectivity, -delta D,L(delta G), -delta D,L(delta H), delta D,L(delta S) and Tiso, have been determined by gas chromatography employing the concept of the retention increment R' for the inhalation anesthetics enflurane (1), isoflurane (2) and desflurane (3) and the selector octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-gamma-cyclodextrin (4) in the polysiloxane SE-54. It is shown that the separation factor alpha is concentration-dependent. Therefore, the separation factor alpha should not be employed as a criterion for enantioselectivity in diluted systems. The -delta DL(delta G) data for 1 and 4 are corroborated by 1H NMR spectroscopic measurements.