Is there a term for a procedure in which the chromatography column is washed with 20% alcohol
Prepared or conditioned for storage would probably be perfectly acceptable.

If you're looking for a single-word equivalent, in this case, I would translate as stabilized. From dictionary.com:


  stabilize  
  
  [stey-buh-lahyz]   
  
  verb (used with object), stabilized, stabilizing.  
  
  
  to make or hold stable, firm, or steadfast.
  


This seems appropriate, since one wants to ensure maintenance of the proper condition of the column for later usage, when taken out of storage.