Cyclodextrin derivatives in GC Separation of racemates of different volatility

Since the end of the ’80, cyclodextrin (CD) derivatives have been shown to be highly effective chiral selectors in gas chromatography [1-3]. Many applications of enantioselective GC with cyclodextrins as stationary phases are from the field of flavour and fragrance [4-6] where the enantiomeric excess and/or ratio determination is a very important task to define not only the biosynthetic pathway or the origin of a compound, but also to evaluate the authenticity of a sample or to detect frauds. Several 6-tert-butyldimethylsilyl cyclodextrin derivatives substituted in position 2 and 3 with the same substituent (homogeneously substituted CDs) were developed for enantioselective analyses but a derivative with a universal enantioselectivity has not yet been found. This study deals with the development of CD derivatives with different substituents in position 2 and 3, i.e. 2-O-ethyl-3-O-methyl-6-O-tBDMS-b-CD (EM) and 2-O-methyl-3-O-ethyl-6-O-tBDMS-b-CD (ME), with the aim of extending the separation capability of homogenously substituted CDs to be applied to enantioselective GC analyses of complex real world samples. More than a hundred standard racemates of chiral molecules of vegetable origin were analysed with the new derivatives and their performance was compared to that of the corresponding homogeneously substituted CDs (i.e. 2,3-di-O-ethyl-6-O-tBDMS-b-CD [7] and 2,3-di-O-methyl-6-O-tBDMS-b-CD [8] ). Real-world samples were also analysed. The new derivatives showed good chromatographic properties and enantioselectivity providing a higher separation capability for the racemate investigated.