Chromatography and
Instrumentation
• Invented by a Russian Botanist Mikhail Tswett
in 1903
• He used chromatography
to separate the colour
pigments in plants from
one another
• Chromatography is a separation technique in
which a mobile phase carrying a mixture
moves in contact with a selectively adsorbent
stationary phase
In English!!!!!
• Chromatography involves two phases
1. A Mobile phase which can move
2. A stationary phase which cannot move
The mixture (such as ink ) is placed on the stationary phase
(such as filter paper) and the mobile phase (such as
water) passes over it. Different parts of the mixture will
have different adherence (attraction) to the stationary
phase and mobile phase, the components of the mixture
which have a better affinity with the mobile phase will
move more easily with the water than those that have a
better affinity with the stationary phase
Uses of Chromatography
• Chromatography was originally used to separate
coloured substances but now is used to separate
a wide variety of different compounds
• It is also used to estimate how much of a
particular component is in a mixture
• For example determining the purity of a drug,
separate out all the components of the drug and
assess how much of the active compound is
present
Types of Chromatography
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Paper Chromatography
Thin Layer Chromatography
Column Chromatography
Gas Chromatography
High Performance Liquid Chromatography
Paper Chromatography
• The stationary phase is chromatography paper
• The mobile phase is a solvent such as
methanol or water etc.
Thin Layer Chromatography
• More efficient than paper chromatography as the
particles in the stationary phase are smaller
• Stationary phase is a thin layer of aluminium
oxide or silica gel spread on a glass plate
• Mobile phase is a solvent
• Spot of mixture is placed at
the end of the plate and then
into the solvent
Thin Layer Chromatography
• It is often used to determine the purity of
drugs or in forensics to separate colours from
dyes extracted from fabrics found at a crime
scene to see if the suspect matches
• In many cases the component being separated
may not be coloured and the plates may be
sprayed with chemicals or looked at with UV
light to make some spots visible
Column Chromatography
• Thr staionary phase is placed
in a long tube or column
• It is commonly made of a solid
adsorbent material such as a
gel
• Glass wool is placed at the end
to prevent the stationary
phase from flowing out
• The mixture to be separated is
dissolved in a solvent and
added at the top the different
components will adhere at
different points to the beads
and form bands which can be
identified
• By adding more solvent
each of the different
bands may be dissolved
out of the column and
collected separately in
beakers
• NB another term for
solvent is Eluent
• Passing a solvent
through the column is
known as elution
Gas Chromatography
• Gas chromatography uses a gas as the mobile
phase
• The stationary phase is a high boiling point
liquid (like a ling chain alkane) spread on solid
particles (alumina or silica gel beads) that are
packed into a column
• This column is kept in an oven and the sample
to be analysed is injected into the hot column
using a syringe
• The sample is vaporised
and carried through the
system by an unreactive
carrier gas
• The various
components are
separated out along the
column based on their
solubility in the solvent
• As each component
leaves the column it
passes into a detector
that records a signal
• This detector then plots
a chart where each
component shows up as
a peak
Uses of Gas Chromatography
• Measure the level of alcohol in blood or urine
samples
• Analyse drug test samples from athletes
High Performance Liquid
Chromatography
HPLC
• In this type of chromatography a pump is used
to force a liquid through a tightly packed
column
• The high temperatures needed in gas
chromatography are not necessary so more
chemicals can be analysed in this way
• The components are detected by a detector
and a chart is produced similar to the method
in Gas Chromatography
Other Important Instrumental
Techniques in Chemistry
• Infra Red Spectrometry
• Ultra Violet Sectrometry
Infra Red Spectrometry
• Infra red spectrometry can be used to identify
organic compounds
• Infra red radiation is emitted by lots of objects
• Different bonds absorb infra red rays of
different wave lengths Eg, A C=C bond would
absorb a different wavelength than an O-H
bond
• Thus every organic compound has a unique IR
spectrum that can serve as a fingerprint for it
IR Spectrum of Polystyrene
Uses of Infra Red Spectrometry
• Identify plastics, illegal drugs etc.
Ultra Violet Spectrometry
• UV spectrometry is used to detect the
presence of certain functional groups in
molecules
• It may also be used to measure the
concentrations of certain organic compounds
in solution Eg, in clinical drug trials samples of
blood may be taken and analysed to see
where the drug is in the body and what is
happening to it