Gas chromatographic enantiomer separation of atropisomeric PCBs using modified cyclodextrins as chiral phases

Columns containing different types of cyclodextrin derivatives have been ev aluated for chiral gas chromatographic separation of atropisomeric PCBs, o, p'-DDT and o,p'-DDD. Separation was attempted on columns containing mixed c hiral selectors, and the performance of two closely related selectors was a lso examined. The cyclodextrins were: permethylated-beta -CD (PM-beta -CD), heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta -CD (2,3-M-6-TB DMS-beta -CD), heptakis(2,3-di-O-methyl-6-O-tert-hexyldimethylisilyl)-beta -CD (2,3-M-6-THDMS-beta -CD), and heptakis(2,3-di-O-ethyl-6-O-tert-hexyldim ethylsilyl)-beta -cyctodextrin (2,3-E-6-THDMS-beta -CD). The cyclodextrins were dissolved in OV-1701 or in a dimethylsiloxane/silarylene copolymer con taining 5% phenyl in the backbone, The application of mixed chiral selector s led to improved separations, however; at most eleven PCB congeners were s eparated on a single column. Chiral resolution of o,p'-DDD was achieved. Th e use of a dimethylsiloxane/silarylene copolymer as a matrix for the cyclod extrins is a promising approach. With such a matrix, blocking of the CD cav ities by silicone substituent groups can be avoided, and a reasonable CD so lubility can be provided. The selectivity of heptakis(2,3-di-O-ethyl-6-O-te rt-hexyldimethylsilyl)-beta -CD and heptakis(2,3-di-O-methyl-6-O-tert-hexyl dimethylsilyl)-beta -CD was quite different, the former selector could sepa rate four congeners, while the latter separated ten congeners.