ENANTIOMERIC SEPARATION BY GC ON CHIRASIL-DEX - SYSTEMATIC STUDY OF CYCLODEXTRIN CONCENTRATION, POLARITY, IMMOBILIZATION, AND COLUMN STABILITY

Polysiloxane-anchored permethylated beta-cyclodextrin (Chirasil-Dex) was used for enantiomeric separation by GC. Four types of Chirasil-Dex, containing up to 36 % permethylated beta-cyclodextrin by weight, were synthesized and compared with 10% permethylated beta-cyclodextrin dissolved in OV-1701. The influence of the cyclodextrin weight percentage on the chiral separation factor alpha and on polarity, as expressed by the Kovats indices, was studied. The chiral separation factors alpha did not increase significantly above a threshold of approximately 30% permethylated beta-cyclodextrin by weight. The plots of alpha vs. weight percentage depend on the complexation strength of the chiral solutes, as do the Kovats indices; for weakly complexing solutes, changes in the cyclodextrin concentration result in larger changes in alpha, but in less pronounced changes in the Kovats indices, as compared to strongly complexing solutes. Column performances were investigated for immobilized and nonimmobilized stationary phases. As expected, immobilization properties were found to depend on the content of Si-H groups in the polysiloxane backbone. Immobilized columns exhibited a much better long-term stability of all chromatographic variables investigated.