We propose phase fluctuation chromatography(PFC) to separate a large amount of random copolymers into fractions with different chemical compositions. PFC is based on the tendency of a concentrated solution of the copolymer to separate into different phases, each of which is enriched with components of a specific composition. When the multiphase solution is injected into a column packed with porous materials that have specific moieties, domains rich in a component with greater affinity to (or less repulsion from) the surface will be retained longer than the domains rich in the other component. Styrene-acrylonitrile copolymers with different acrylonitrile contents were used as model copolymers. The compositions of fractions obtained were determined from IR spectra. A silanol or diphenyl surface retained styrene-rich components longer than the other components, whereas a cyano surface attracted acrylonitrile-rich components. The separation resolution was better when the pore had a large surface area and selective surface moieties and when selective solvents and higher concentrations were used.