A Paper-Chromatography Model

In paper chromatography, a spot of ink is placed near the bottom of paper. The paper’s lower edge sits in a shallow solvent, with the ink spot above the liquid. The solvent travels up through the paper. It dissolves some ink components and carries them along. Components that dissolve more readily in the solvent and are less attracted to the paper usually travel farther. Different components can form separate colored bands. The solvent is called the mobile phase because it moves; the paper is the stationary phase because it stays in place. This model separates parts of a mixture—it does not create new colors. Different substances can sometimes produce similar band patterns, so matching patterns are useful evidence but do not prove identity by themselves.