The present invention is a method of producing a chromatographic separation matrix, wherein porous polymeric particles comprised of two layers with different properties are prepared in a two-phase system by (a) providing porous polymeric particles with reactive groups on their surfaces; (b) washing said particles with a first solvent and draining the particles to enclose a first phase; (c) wetting the outer layer of the particles by adding a second solvent, which is essentially insoluble in the first solvent; (d) reacting the reactive groups in the outer layer by adding a reagent, which is essentially non-reactive in the first solvent; and (e) coupling of chromatographic binding groups to the reactive groups in the inner layer. The invention also encompasses a porous polymer particle suitable for use as a chromatographic separation matrix and a process of separation, wherein a matrix according to the invention is used.