Chromatography
Partition
In IB chemistry, partition is all about differences in and relative solubilities of components in a sample which causes them to dissolve and partition onto the stationary or mobile phases accordingly. The more soluble/ volatile the component, the faster it moves.
Stationary phase: non-volatile liquid
Mobile phase: inert solid surface
Examples: paper chromatography and gas liquid chromatography.
Adsorption chromatography
Adsorption is all about relative bonding and reactivity with the stationary and mobile phases. Some components of the mixture are attracted to the solid surface and the other components are less strongly attracted to the stationary phase travel faster with the mobile phase.
Stationary phase: solid stationary phase
Mobile phase: liquid or gas phase
Examples: Thin-layer chromatography.
Paper chromatography
Stationary phase: chromatographic adsorbent paper
Mobile phase: suitable solvent (water/ ethanol)
A small spot is placed on the chromatographic paper which is dipped in the solvent. The component spots dissolve in the solvent and move up with the solvent, moving different distances depending on their solubilities. The solvent front marks the maximum distance moved by the solvent in IB chemistry. The chromatogram is finally treated with a dye/ UV light if the different components aren't visible e.g. ninhydrin to identify amino acids.
R_f value: this is the (distance moved by the component from the base line) / (distance moved by the solvent front).
Limitations: Components having similar R_f values are indistinguishable, unknown/ new substances have no R_f values to test against according to IB chemistry curriculum.
End of this topic!
