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
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
