What is the Difference Between Stationary and Mobile Phase?

The main difference between stationary and mobile phases in chromatography lies in their movement and interaction with the sample. Here are the key differences:

Stationary Phase: This phase remains fixed in place and does not move with the sample. It can be a solid or liquid, supported on a solid support material, such as silica or alumina. The stationary phase acts as a constraint on many components in a mixture, slowing them down to move slower than the mobile phase.
Mobile Phase: This phase moves with the sample and carries the components through the medium being used. The mobile phase is typically a gas or a liquid, such as an inert gas or a solvent. It is responsible for dissolving the components of the sample and carrying them through the stationary phase.

In chromatography, the mobile phase moves through the stationary phase, and the components of the mixture interact with both phases. The movement of the components in the mobile phase is controlled by the significance of their interactions with the stationary phase. The polarity of the components in the sample determines which phase they will interact with more, allowing for the separation of moderately polar and nonpolar components.

For example, in gas chromatography, the stationary phase is a solid or liquid coated on the inner surface of a column, while the mobile phase is a chemically inert gas that carries the molecules of the analyte through the column. In high performance liquid chromatography (HPLC), the stationary phase can be a solid or liquid supported on a solid support material, and the mobile phase is a liquid or a supercritical fluid.