Determination and use of Rohrschneider-McReynolds constants for chiral stationary phases used in capillary gas chromatography.

The overall polarity of 22 chiral stationary phases (CSPs) used in capillary open tubular gas chromatography columns was estimated using the first five Rohrschneider-McReynolds constants. Most of the columns (i.e., 18) were wall-coated, and four were of the wall-immobilized or of the so-called "bonded" type. A wall-coated capillary squalane column was specially prepared as a polarity reference column. All but two of the CSPs were based on derivatized cyclodextrins (CDs) of different sizes. The overall properties of the CSPs are discussed in terms of the five Rohrschneider-McReynolds constants and their average values. It was found that the derivatized cyclodextrin CSP polarity increased with the CD ring size. The bonded CSPs were significantly less polar than their coated homologues due to the apolar polymer used to immobilize the CD rings. The retention behavior of 14 compounds was studied at 100 degrees C on the capillary columns. Retention parameters are clearly related to the McReynolds constants. Conversely, the enantiomeric resolution capability of a given stationary phase is not related to the constants. The enantioselective resolution mechanism critically depends on the solute structure and on the nature of the CSP.