Why do some substances travel through a chromatographic column more slowly than others?

In chromatography, substances travel through a column at different rates because they distribute themselves between the stationary phase and the mobile phase based on their relative affinities for each.12

The rate of travel is determined by the strength of the intermolecular forces between the solute molecules and the stationary phase. Components that are more strongly attracted to the stationary phase are held back, requiring more time to be eluted from the column. Conversely, components that have a weaker attraction to the stationary phase—or a stronger affinity for the mobile phase—are flushed through the system more rapidly.31

In addition to these chemical attractions, physical mechanisms can influence migration speeds. For example, in size-exclusion chromatography, molecules are retained based on their ability to penetrate the pores of the stationary phase; smaller molecules that enter the pores travel more slowly, while larger molecules that are excluded from the pores elute first.4