Final answer:
The method that can NOT be used to separate a mixture of enantiomers is chiral column chromatography.
Step-by-step explanation:
The method that can NOT be used to separate a mixture of enantiomers is C. chiral column chromatography.
Chiral column chromatography is a separation technique that involves using a stationary phase with chiral properties to separate enantiomers. The stationary phase contains a chiral resolving agent, which interacts differently with the enantiomers based on their specific chirality. This allows for the separation of the enantiomers. However, if a mixture of enantiomers is already separated, chiral column chromatography would not be needed, as it is a method used specifically for separating enantiomers.