In chromatography, what does the 'stationary phase' refer to?

In chromatography, the 'stationary phase' refers to the fixed substance on which mixtures are separated. This phase is crucial for the separation process because it provides a medium for the components of the mixture to interact with. When a sample is introduced, the various components will adhere to this solid or liquid layer to different extents based on their chemical properties, such as polarity or size.

As the mobile phase (which is the moving solvent or gas) flows through or over the stationary phase, the different components of the mixture travel at different rates. Those that interact more strongly with the stationary phase will move more slowly, while those that interact less will move faster. This differential movement results in the separation of the various components in the mixture.

The stationary phase is therefore an essential concept in understanding how chromatography works, as it is this fixed nature that allows for the separation based on different affinities between the components and the stationary phase.