General requirements • A packing material serves to form the chromatographic bed. It may or may not be involved in the actual separation process (i.e., distribution of a solute between two phases). • In classical liquid-liquid chromatography, the packing serves only to support the stationary phase, which is the liquid that resides in its pores. • However, in adsorptive modes of chromatography, including ion-exchange and affinity, the column packing material simultaneously serves as both support and stationary phase.