The Collaborative International Dictionary of English v.0.48:

Fractionate \Frac"tion*ate\, v. t.
   To separate (a mixture of chemical substances) into different
   portions or fractions, as in the distillation of liquids.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fractionate
    v 1: separate into constituents or fractions containing
         concentrated constituents
    2: obtain by a fractional process

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "fractionate":
   aerate, aerify, atomize, carbonate, chlorinate, distill, emit,
   etherify, etherize, evaporate, exhale, fluidize, fume, fumigate,
   gasify, give off, hydrogenate, oxygenate, perfume, reek, send out,
   smoke, spray, steam, sublimate, sublime, vaporize, volatilize