Thin-Layer Chromatography (TLC) Uses: • To separate the components of a mixture • To determine the purity of a compound • To see if two compounds are identical • To monitor the progress of a reaction A separation/purification technique. Chromatography
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Thin-Layer Chromatography (TLC) Uses: To separate the components of a mixture
Chromatography. A separation/purification technique. Thin-Layer Chromatography (TLC) Uses: To separate the components of a mixture To determine the purity of a compound To see if two compounds are identical To monitor the progress of a reaction. Thin-Layer Chromatography. Filter Paper. - PowerPoint PPT Presentation
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Thin-Layer Chromatography (TLC)
Uses:• To separate the components of a mixture • To determine the purity of a compound • To see if two compounds are identical • To monitor the progress of a reaction
A separation/purification technique.
Chromatography
Thin-Layer Chromatography
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TLC Bottle/Chamber
Filter Paper
TLC Plate: containsA polar stationary phase(alumina or silica gel) &a very small amountof your sample
Mobile Phase: organic solvent(s) of varying polarity
Chromatography Basics
How it works:
• Your sample is loaded onto the polar stationary phase• Polar compounds will adsorb onto the stationary phase to a greater extent than non-polar compounds• The mobile phase (eluting phase) helps “push” or elute the compounds either down a column (for CC) or up a plate (for TLC)
The main concept to consider in chromatography is polarity.
Polarity & Intermolecular Attractive Forces
• More polar compounds will be more attracted to silica gel than non-polar compounds due to intermolecular attractive forces - a dipole-dipole interaction.
• The more non-polar compounds will travel more easily and more quickly through the stationary phase.• The mobile phase helps carry the compounds through the stationary phase.
Separation of compounds in a mixture is possible because compoundshave different polarities.
Si
OH
O
O
O
Siδ+
δ-
δ-
δ-
δ+
Silica gel, [SiO2]n
Polarity & Intermolecular Attractive Forces
Example: Separate a mixture of butyl amine and cyclohexane using TLC
Things to consider:1. Polarity of each compound in the mixture
Butyl amine is polar; cyclohexane is non-polar2. Polarity of stationary phase
Silica gel (or alumina) is polar - predict that butyl amine willinteract with it more strongly
3. Polarity of the mobile phase - the solvent: you determine what solvent to use
Si
OOδ+
δ-
N
H
Hδ-δ+
H2C
H2CCH2
CH2
CH2
H2C
Prediction:Cyclohexane will elutefirst/faster through the stationaryphase.Butyl amine will elute last/slower.
TLC Separation
Example: Separate a mixture of butyl amine and cyclohexane using TLC
Si
OOδ+
δ-
N
H
Hδ-δ+
H2C
H2CCH2
CH2
CH2
H2C
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Mobile Phase: Typically use a mixed solventsystem. If the mobile phase is non-polar,cyclohexane will travel along with it, butbutyl amine will not as readily.If the mobile phase is polar, both cyclohexaneand butyl amine will travel with it, butbutyl amine will be slower because it’ll beinteracting with silica gel as it’s traveling.
Note the separationof spots
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Chapter 13: TLC Experiment/Separation of ChlorophyllThe Experimental Steps
(a) Dissolve sample in asmall amount of organic solvent
(b) Use capillary tubes to load onsample
TLC plate (labeled)with samples loaded
depth of mobile phase
Ac As C I
Aceaminophen spot
Aspirin spot
Caffeine spot
Ibuprofen spot
pencil mark 1 cmfrom bottom
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2. Insert TLC plate into TLC chamber (filled with a layer of mobile phase & allow mobile phase to “run up” the TLC plate. Take out when the solvent reaches 1 cm from top of plate (solvent front). Mark the solvent front line with a pencil.
Origin Line
Solvent Front Line
Distance traveledby solvent
Distance traveled by spot
Rf = distance spot traveled from origin line/distance of solvent front