The present invention relates to a method of preparing a separation medium starting with an aqueous solution of spherical and preferably functionalised primary particles of defined size, comprising the following steps: a) inverse suspension dispersing said aqueous solution of primary particles as droplets in oil; b) evaporation to remove said aqueous solution and fusion between particles to form spherical aggregates; c) size fractionation of aggregates from step b); and optionally d) repeating steps a) to c) an optional number of times to form progressively larger spherical aggregates. The invention also relates to a separation medium produced by this method. The present separation medium can be used in chromatography in the form of essentially spherical aggregates in packed or expanded bed columns or in the form of assembled aggregates on a support for filtration purposes.