Chromatography

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  • Created by: Hindleyc
  • Created on: 19-04-19 13:33
What is Chromatography
is an analytical technique that separates components in a mixture between a mobile phase and a stationary phase.
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Types of chromatography include:
thin-layer chromatography (TLC) , thin-layer chromatography (TLC) , gas chromatography (GC)
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What is TLC
a plate is coated with a solid and a solvent moves up the plate
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What is CC
a column is packed with a solid and a solvent moves down the column
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What is GC
a column is packed with a solid or with a solid coated by a liquid, and a gas is passed through the column under pressure at high temperature.
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What may The mobile phase may be
a liquid or a gas.
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The stationary phase may be
a solid (as in thin- layer chromatography, TLC) or either a liquid or solid on a solid support (as in gas chromatography, GC)
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In gas-liquid chromatography GC the mobile phase is a
a inert gas such as nitrogen, helium, argon.
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The Stationary phase is a
liquid on an inert solid.
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Separation by column chromatography depends on
the balance between solubility in the moving phase and retention in the stationary phase.
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If the stationary phase was polar and the moving phase was non- polar e.g. Hexane. Then non- polar compounds would pass through the column
more quickly than polar compounds as they would have a greater solubility in the non-polar moving phase.
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A solid stationary phase separates by ,
adsorption
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A liquid stationary phase separates by
relative solubility
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Retention times and Rf values are used to identify
different substances.
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How do you do TLC
a) Wearing gloves, draw a pencil line 1 cm above the bottom of a TLC plate and mark spots for each sample, equally spaced along line. b) Use a capillary tube to add a tiny drop of each solution to a different spot and allow the plate to air dry.
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Then
c) Add solvent to a chamber or large beaker with a lid so that is no more than 1cm in depth d) Place the TLC plate into the chamber, making sure that the level of the solvent is below the pencil line. Replace the lid to get a tight seal.
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Then
e) When the level of the solvent reaches about 1 cm from the top of the plate, remove the plate and mark the solvent level with a pencil. Allow the plate to dry in the fume cupboard. f) Place the plate under a UV lamp in order to see the spots.
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Finally
Draw around them lightly in pencil. g) Calculate the Rf values of the observed spots.
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What will Wear plastic gloves prevent
contamination from the hands to the plate
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pencil line –
–will not dissolve in the solvent
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tiny drop
too big a drop will cause different spots to merge
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Depth of solvent–
if the solvent is too deep it will dissolve the sample spots from the plate
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lid–
to prevent evaporation of toxic solvent
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How Will get more accurate results
if the solvent is allowed to rise to near the top of the plate
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but the Rf value can be calculated if
the solvent front does not reach the top of the plate
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dry in a fume cupboard as
the solvent is toxic
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UV lamp used if the spots are
colourless and not visible
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Rf value =
distance moved by amino acid/ distance moved by the solvent
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What is Simple column chromatography
A glass tube is filled with the stationary phase usually silica or alumina in powder form to increase the surface area. • A filter or plug is used to retain the solid in the tube. Solvent is added to cover all the powder.
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then
• The mixture to be analysed is dissolved in a minimum of a solvent and added to the column. • A solvent or mixture of solvents is then run through the column. • The time for each component in the mixture to reach the end of the column is recorded
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What is this called
retention time
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HPLC stands for
high performance liquid chromatography and it type of column chromatography commonly used in industry.
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HPLC: stationary phase
is a solid silica
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HPLC: mobile phase
a liquid
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What can Gas-liquid chromatography can be used to
separate mixtures of volatile liquids.
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In gas-liquid chromatography, the mobile phase is
a gas such as helium
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and the stationary phase is
a high boiling point liquid absorbed onto a solid.
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retention time.
The time taken for a particular compound to travel from the injection of the sample to where it leaves the column to the detector
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This can be used to
identify a substance.
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Some compounds have
similar retention times so will not be distinguished.
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Basic gas-liquid chromatography will tell us
how many components there are in the mixture by the number of peaks.
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It will also tell us
the abundance of each substance.
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The area under each peak will be proportional to
the abundance of that component.
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It is also possible for gas-liquid chromatography machine to be connected to a
mass spectrometer, IR or NMR machine,
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What does this enable
all the components in a mixture to be identified.
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GC-MS is used in
analysis, in forensics, environmental analysis, airport security and space probes.
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Most commonly a mass spectrometer is combined with GC to generate a
mass spectra which can be analysed or compared with a spectral database by computer for positive identification of each component in the mixture.
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Other cards in this set

Card 2

Front

Types of chromatography include:

Back

thin-layer chromatography (TLC) , thin-layer chromatography (TLC) , gas chromatography (GC)

Card 3

Front

What is TLC

Back

Preview of the front of card 3

Card 4

Front

What is CC

Back

Preview of the front of card 4

Card 5

Front

What is GC

Back

Preview of the front of card 5
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