Summary Chromatography Notes - AQA Chemistry A Level

Chromatography
 Substances separated according to relative affinity to the stationary and mobile phase
o Stronger affinity for mobile phase – more quickly
o Stronger affinity for stationary phase – move slowly
 Stationary phase – SiO2 (silica) and Al2O3 (alumina) are regarded as polar powders, and so attract
polar substances
 Mobile phase – non polar solvents (alkanes), polar solvents (water, alcohols)
 E.g. hexane as solvent on silica
o Non-polar molecules move quickly
o Polar molecules move slowly

Thin Layer Chromatography (TLC)
 Stationary – powder (SiO2 or Al2O3)
 Mobile – solvent
 Lid – atmosphere must be saturated in solvent to prevent full evaporation
 Colourless samples – view results under UV light
 Amino acids can be stained by ninhydrin
𝑑𝑖𝑠 tan 𝑐 𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑𝑏𝑦 𝑠𝑎𝑚𝑝𝑙𝑒
 Rf =
𝑑𝑖𝑠 tan 𝑐 𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑 𝑏𝑦 𝑠𝑜𝑙𝑣𝑒𝑛𝑡

Column Chromatography
 ‘Large scale TLC’
 Stationary – powder (SiO2 or Al2O3)
 Mobile – solvent






Gas Chromatography
 Stationary – long coiled tube packed with powder
 Mobile – inert gas passes through the tube