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

The 2,3-di-O-methyl-, 2,3-di-O-ethyl-, and 2,3-di-O-acetyl- derivatives of 6-t-hexyldimethylsilyl-beta- and -gamma-cyclodextrins (THDMS-beta- and -gam ma-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 di fferent structures and volatilities. The results obtained with THDMS-beta- and -gamma-CDs were compared with those of the corresponding 6-O-t-butyldim ethylsilyl-beta- and -gamma derivatives (TBDMS-beta- and -gamma-CDs) to eva luate the influence on enantioselectivity of the substituent in position 6 of the sugar units of the two cyclodextrins. Columns prepared with both ser ies of derivatives (THDMS- and TBDMS-beta- and -gamma-CDs) were evaluated b y analyzing a series of high-to-medium volatility racemates and of medium-t o-low volatility chiral pesticides. For high-to-medium volatility racemates , the TBDMS-beta-CDs are the most enantioselective, while for medium-to-low volatility racemates the THDMS-gamma-CDs have a better enantioselectivity than the corresponding TBDMS-beta-CDs, (C) 1999 John Wiley & Sons, Inc.