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Courtesy of ASTEC Inc. Figure 18 The Separation of Warfarin Isomers on a CYCLOBOND Column The cyclodextrins are produced by the partial degradation of starch followed by the enzymatic coupling of the glucose units into crystalline, homogeneous toroidal structures of different molecular sizes. Three of the most widely characterized are alpha, beta and gamma cyclodextrins which contain 6, 7 and 8 glucose units respectively. Cyclodextrins are chiral structures and the beta- cyclodextrin has 35 stereogenic centers. CYCLOBOND is a trade

of cycles, as significant peak dispersion can occur each time it passes through the pump. Nevertheless, there is a substantial net gain in resolution on each cycle. This procedure can be very time consuming if long retention times are involved, but has the great advantage of solvent economy. The recycling procedure, in effect, artificially increases the column length and actually trades in time for solvent economy.  An example of the recycling process is demonstrated in the separation of the Warfarin enantiomers shown in figure 20. The separation was carried out on a CYCLOBOND 1 2000 column, 25 cm long, 1 in, I.D., using a mobile phase consisting of methanol/acetic acid/triethylamine : 100/0.3/0.2 v/v/v, at a flow rate of 12 ml/min.   Courtesy of ASTEC Inc.   Figure 20 The Separation of the Warfarin Enantiomers by Recycling