GC and HPLC are instrumental chromatographic techniques - Leaving Cert Chemistry - Question h - 2019

The principle of separation in chromatography is based on the different interactions that components of a mixture have with the stationary phase and the mobile phase. Components in a mixture are differentially partitioned or dissolved between these two phases due to their distinct affinities, which can be influenced by interactions such as adsorption, solubility, and polarity.

In chromatography, the mobile phase carries the mixture through the stationary phase. As the mixture moves, each component selectively interacts with the stationary phase, which retains them to varying degrees. This results in components passing through the stationary phase at different speeds, leading to their separation.

To summarize, the separation occurs because:

1. Components have different attractions (affinities, interactions, solubilities) for the stationary and mobile phases.
2. Components are differentially partitioned between the stationary phase (where they may be adsorbed or retained) and the mobile phase (which carries them along).
3. Components elute or pass through the stationary phase at different rates, allowing for separation over time.