Cyclodextrin derivatives in gas chromatographic separation of racemates with different volatility. Part XV: 6-O-t-butyldimethylsilyl- versus 6-O-t-hexyldimethylsilyl-? and -? derivatives

The 2,3-di-O-methyl-, 2,3-di-O-ethyl-, and 2,3-di-O-acetyl- derivatives of 6-t-hexyldimethylsilyl-β- and -γ-cyclodextrins (THDMS-β- and -γ-CDs) were synthesized. The performance of columns prepared with these CD derivatives diluted in polysiloxanes with different polarity (PS-347.5, PS-086, and OV-1701) was evaluated with several series of racemates having different structures and volatilities. The results obtained with THDMS-β- and -γ-CDs were compared with those of the corresponding 6-O-t-butyldimethylsilyl-β- and -γ derivatives (TBDMS-β- and -γ-CDs) to evaluate the influence on enantioselectivity of the substituent in position 6 of the sugar units of the two cyclodextrins. Columns prepared with both series of derivatives (THDMS- and TBDMS-β- and -γ-CDs) were evaluated by analyzing a series of high-to-medium volatility racemates and of medium-to-low volatility chiral pesticides. For high-to-medium volatility racemates, the TBDMS-β-CDs are the most enantioselective, while for medium-to-low volatility racemates the THDMS-γ-CDs have a better enantioselectivity than the corresponding TBDMS-β-CDs.