Preparative Chromatography - Recycling Development > Page 41

The separation of a simple binary mixture of chiral isomers is an excellent example of the type of separation for which the recycling technique is particularly useful. The chromatogram shows the results obtained from three complete elution cycles. In the first cycle, although separation has begun, there is little or no visible resolution. It should also be noted that the peak is distinctly asymmetrical. On the second cycle, the two enantiomers are beginning to separate and the asymmetry is at least as bad if not worse. In the third cycle, the separation is improved still further, and is sufficient to allow the collection of significant quantities of the individual isomers at a high purity despite the asymmetry. It is also seen that the process is fairly rapid as three cycles are completed in less than 12 minutes.

An additional example of the technique of recycling, which includes another collection procedure called peak shaving, is shown in figure 21 which depicts the preparative separation of the enantiomers of 5-methyl-5-phenylhydantoin. The recycling and peak shaving procedure is included in figure 21.


Courtesy of ASTEC Inc.


Figure 21. The Preparative Separation of the Enantiomers of 3-Methyl-5-Phenylhdantoin