ketamine isolation from amine mixture

[heavenadisaster]

There are a couple of grams a mixture of gabapentin, cyclobenzaprine, lidocaine and ketamine.  Is there any way around column chromatography to separate these components?

There solubilities seem too similar to get away with using solvent mixtures, but would it be possible to use the differences in their pka's to sort them into polar and non-polar liquids phases through controlling pH?

Any suggestions or experience would be helpful.