In chromatographic separation, two different phases are important; a stationary phase and a mobile phase.
The stationary phase is the phase that does not move. Substances are separated based on how fast or slowly they move in the stationary phase.
The mobile phase is usually the solvent(or mixture of solvents) that carries the solutes through the stationary phase.
The stationary phase is usually composed of a porous material. Paper is a porous material. The mobile phase is trapped between the cellulose fibers of the paper and separation is achieved.
