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A2 1098
17-Jul-16
Type
Stationary Phase
Mobile Phase
Column
Powder (SiO2 or Al2O3)
solvent
Paper
(simple TLC)
Absorbent paper
solvent
TLC
Powder (SiO2 or Al2O3) on
glass/plastic plate
solvent
Gas
Powder (SiO2 or Al2O3)
(sometimes coated with liquid)
Inert gas
(e.g. Ar, N2)
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A2 1095
17-Jul-16
In ALL chromatography
Substances separated according to relative affinity
(attraction) to stationary and mobile phase.
If stronger affinity for mobile phase, then move quickly
If stronger affinity for stationary phase, the move slowly
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A2 1095
17-Jul-16
STATIONARY PHASE:
SiO2 (silica) and Al2O3 (alumina) are regarded as a polar
powder (due to the nature of their surface structure)
MOBILE PHASE:
Non-polar solvents: alkanes
Polar solvents: water, alcohols
e.g. hexane as solvent on silica
non-polar molecules would move quickly
polar molecules would move slowly
© www.chemsheets.co.uk
A2 1095
17-Jul-16
© www.chemsheets.co.uk
A2 1095
17-Jul-16
Stationary:
Powder (SiO2 or Al2O3)
Mobile:
Solvent
For colourless samples:
View results under UV light
Amino acids
can be stained using ninhydrin
solvent front
5 cm
4 cm
For substance R
Rf = 3 = 0.6
5
For substance S
Rf = 4 = 0.8
5
3 cm
starting line
R
S
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A2 1095
17-Jul-16
© www.chemsheets.co.uk
A2 1095
17-Jul-16
“Large scale TLC”
Stationary:
Powder (SiO2 or Al2O3)
Mobile:
Solvent
FROM: http://www.mun.ca/biology/scarr/4241_RCMchromatogrpahy.jpg
FROM: wikipedia
© www.chemsheets.co.uk
A2 1095
17-Jul-16
• Long coiled tube packed with powder.
• Inert gas passes through tube
• Retention time = time to travel
through tube
• Samples often analysed by mass
spectrometer as they leave tube
Gas chromatogram (e.g. of a fraction of crude oil)