Ionic liquids as stationary phase solvents for methylated cyclodextrins ingas chromatography

Room temperature ionic liquids (RTIL) are molten salts with melting points well below room temperature. 1-butyl-3-methylimidazolium chloride is a typi cal example of such RTIL. It was used as a solvent to dissolve permethylate d-beta -cyclodextrin (BPM) and dimethylated-beta cyclodextrin (BDM) to prep are stationary phases for capillary columns in gas chromatography for chira l separation. The RTIL containing columns were compared to commercial colum ns containing the same chiral selectors. A set of 64 chiral compounds separ ated by the commercial BPM column was tested on the RTIL BPM column. Only 2 1 were enantioresolved. Similarly, a set of 80 compounds separated by the c ommercial BDM column was passed on the RTIL BDM column with only 16 positiv e separations. it is proposed that the imidazolium ion pair could make an i nclusion complex with the cyclodextrin cavity, blocking it for chiral recog nition. All the chiral compounds recognized by the RTIL columns had their a symmetric carbon that was part of a ring structure. The retention factors o f the derivatized solutes were lower on the RTIL columns than those obtaine d on the commercial equivalent column. The peak efficiencies obtained with the RTIL capillary were significantly higher than that obtained with the co mmercial column. These observations may contribute to the knowledge of the mechanism of cyclodextrin-based GC enantioselective separations.