Full, in-depth BTEC Applied Science Unit 2C - Undertake chromatographic techniques to identify components in mixtures coursework.
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Chromatography
In chemistry, you must isolate one substance from another to analyse the substance further
or to prepare it for use in other ways. Chromatography is a process used for separating
mixtures and identifying substances. It can be used to determine a substance's purity.
The mixture is dissolved in a fluid solvent (gas or liquid) called the mobile phase, which is
then carried through a system (a column, a capillary tube, a plate, or a sheet) on which a
material called the stationary phase is fixed. Each substance within a mixture travel at
different velocities in mobile fluid causing them to separate.
Types of chromatography
Paper Chromatography
This type of chromatography is often used to check the purity of pharmaceuticals, detecting
adulterants and to inspect cosmetics. In this type of chromatography, the stationary phase is
paper, and the mobile phase is either an aqueous liquid or a carbon-based solvent such as
propanone. For each chemical in the sample, the separation depends on how strongly
attracted the chemicals components are to the mobile and stationary phase. The paper
itself has a thin coating of water molecules due to the cellulose fibres absorbing moisture
from the air, which may have some minor effects on the results.
Thin Layer Chromatography (TLC)
This type of chromatography is used to analyse dyes in fibres, inks and paints. It is also used
in the detection of pesticides and insecticides in food products. TLC is very similar to paper
chromatography but instead of paper, the stationary phase is a thin layer of an unreactive
substance such as silica or aluminium oxide on a flat surface such as glass, metal or plastic.
Each component of the mixture used is absorbed on the solid. Some components will be
carried further up the plate than others due to their difference in solubility and the strength
of their absorption to the stationary phase. May need to use an ultra-violet lamp to see
colourless samples.
Risk Assesssment
Hazard Risk Precaution First Aid
Broken glass Cuts Always keep glass in Clean the wound by
middle of table to rinsing it with
prevent it from bottled or tap water,
being knocked off or by using sterile
the table. Clear up wipes. If there's
any broken glass nothing in the
immediately. wound, put pressure
on it using a
bandage for 10
minutes. When the
bleeding has
, stopped, put on a
sterile dressing or a
plaster.
Propanone Highly flammable Keep away from In the event of a
Serious eye and skin open flames spillage, it is
irritation Wear a long sleeve essential to clean it
Odor may cause lab coat and gloves up immediately. Use
headaches to protect your skin. appropriate
Wear goggles to absorbent materials,
protect your eyes. such as spill pads or
Use appropriate absorbent socks, to
containers or vessels soak up the spilled
with lids or covers to propanone. Dispose
prevent propanone of the absorbed
from spilling onto material
the surrounding appropriately.
surfaces. If in contact with
Use in a well- skin rinse
ventilated room. immediately.
Ninhydrin Skin, eye and Wear a long sleeve In the event of a
respiratory irritation lab coat and gloves spillage, it is
Harmful if to protect your skin. essential to clean it
swallowed Wear goggles to up immediately. Use
protect your eyes. appropriate
Use appropriate absorbent materials,
containers or vessels such as spill pads or
with lids or covers to absorbent socks, to
prevent ninhydrin soak up the spilled
from spilling onto ninhydrin. Dispose
the surrounding of the absorbed
surfaces. material
Use in a well- appropriately.
ventilated room. If in contact with
skin rinse
immediately.
Spillages Slipping Wipe any spillages Place a cold
immediately to compress or ice pack
prevent people from on any bumps or
slipping and injuring
bruises.
themselves.
Give ibuprofen for
pain if the person is
, alert.
Let the person rest
for the next few
hours if needed.
1. Draw a pencil line across the chromatography paper, 1 to 2 cm from the bottom.
2. Use a capillary tube to add small spots of the plant pigment onto the line on the
paper.
3. Place the paper into a container with a suitable solvent in the bottom such as
propanone.
4. Allow the solvent to move through the paper.
5. Before the solvent reaches the top of the paper, mark the height reached by the
solvent with a pencil.
6. Remove the chromatogram.
7. Allow the chromatogram to dry, then measure the distance travelled by each spot
and by the solvent.
8. Calculate the Rf value.
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