# What does all chromatography have in common?

We're learning about chromatography in class, and I'm confused about all the different types (e.g. those that separate liquid-liquid solutions vs. those that separate liquid-solid solutions vs. those that separate solid-solid solutions, etc.).

Could you provide a summary of the similarities between all forms of chromatography? (just an overview, do not require specifics)

Thanks.

Here are some similarities:

• There is always a mobile (e. g. Gas - GC, Liquid - HPLC; GPC) and a stationary phase (liquid; gel - GC, solid - LCs, GPC).
• Compounds in the sample interact different with both phases and are therefore held back stronger or lesser. This results in the accumulation of compounds that interact similar at some point in the system $-$ with some chromatographys, especially affinity chromatography, one might even get pure substances.
• The mobile phase carrys the sample and is commonly less polar than the stationary phase, except for RPCs.
• The structure of a chromatograph is basically like this:

1. transport system: reproductive transport of the mobile phase, adjustable (e. g. piston pump - LCs, compressed gas cylinder - GC)
2. sample application: import of the sample into the flowing mobile phase (e. g. injector, valve)
3. column: stationary phase and its mounting (e. g. capillary column in the column oven)
4. detector: transformation of the chemical or physical properties, which change with substance concentration, into electrical signals (e. g. UV/VIS-detector, thermal conductivity detector)
5. plotting unit: visualisation of the electrical signals (e. g. integrator, computer)