3-Methyl-5-Phenylhydantoin

The aromatic rings will allow induced dipole interactions with the stationary phase and conversely, the strong polar groups on the stationary phase can induce dipole interaction with polarizable groups on the solute. The cavities are more shallow than those in the cyclodextrins and thus interactions are weaker however, this allows more rapid solute exchange between the phases, and, thus, higher column efficiencies. An example of the use of the stationary phase to separate the enantiomers of 3-methyl-5-phenylhydantoin is shown in figure 54.

to 1.85 min.	to 2.80 min.
k1 0.78	k1 1.57
k2 1.32	k2 2.13
a 1.69	a 1.35
R 2.18	R 3.0

Courtesy of ASTEC Inc.

Figure 54 The Separation of the Enantiomers of 3-Methyl-5-Phenylhydantoin Using Polar and Dispersive Interactions

The separation is carried out under two conditions, the first used pure ethanol as the mobile phase, which is relatively dispersive, and in the second, a mobile phase that contains 90% of water that is strongly polar. Pure ethanol provides extremely strong dispersive interactions in the mobile phase relative to that of the aqueous solvent will be significantly more dispersive than any interactions involved with the stationary phase.

It follows that the remaining dominant retentive forces will be polar or ionic in nature. In the second case, the mobile phase is predominantly water and, thus, provides very strong polar interactions with the solute but very weak dispersive interactions. It also follows, that the retention forces of the stationary phase, in this case, will be dominantly dispersive in nature. This demonstrates the very useful selective flexibility of Vancomycin. By adjusting the mobile phase composition, selectivity can be made to depend largely on dispersive interactions (hydrophobic) or, alternatively, to depend largely on polar interactions (hydrophilic).