What is the separation of molecules on or through a stationary phase called?

The separation of molecules on or through a stationary phase is called chromatography. This technique relies on the differential distribution of compounds between a stationary phase and a mobile phase, allowing for the separation based on various properties such as size, charge, or affinity. During chromatography, the mixture of molecules is applied to the stationary phase, and as the mobile phase moves through or along the stationary phase, different components travel at different rates, facilitating their separation.

In contrast, spectrophotometry is a technique that measures how much a chemical substance absorbs light by using the property of light absorption at particular wavelengths. Activity assays evaluate the functional activity of a specific target, often in biochemical contexts, such as enzyme assays. PK/PD assays assess the pharmacokinetics (how a drug is processed in the body) and pharmacodynamics (the effects of the drug on the body) of drugs. These methodologies do not focus on the separation of molecules akin to chromatography, establishing chromatography as the correct choice for this question.