thin-layer chromatography (tlc) uses: to separate the components of a mixture

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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

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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

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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

1. Load sample onto stationary phase/TLC plate (labeled)

(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