Chromatography involves a sample (or sample extract) dissolved in a mobile phase (a gas, a liquid, or a supercritical fluid). The mobile phase is then forced through an immobile, immiscible stationary phase. The phases are chosen so that components of the sample have differing solubilities in each phase. As a result of these differences in solubilities, sample components will become separated from each other as they travel through the stationary phase. This process, in addition to separating components, also permits analysis. See also High Pressure Liquid Chromatography.