1
Unit 2: Practical Scientific Procedures and Techniques
C: To classify components in mixtures, using chromatographic methods
Separate to identify
Ajmal Shekeb NOORMAL
, Unit 2C Ajmal Shekeb NOORMAL
Scenario
I'm a newly hired technical assistant at Chemcalequip, a big chemical plant. I must
demonstrate skills in a variety of practical procedures and techniques as part of my
induction period and in order to advance in my position. Identifying substances is a common
task for the firm.
I need to show that I can isolate and classify components in mixtures using various
chromatographic techniques. I'll need to clarify the techniques, analyse and assess my
performance, and make suggestions for changes in a report on the techniques I've used.
Chromatography is an analytical method used to separate coloured chemicals or substances.
Chromatography is used in industrial processes to: purify chemicals, test for trace number of
substances, separate compounds and test products for quality control. Capillary action is a
process in which liquid flows in a narrow space without the help of gravity or the opposing
external force. Liquids can be drawn between brush bristles, in thin tubes, in porous materials
such as sand and liquefied carbon fibre, or in biological cells. The intermolecular force
between the liquid and the surrounding solid surface triggers it. Different components of the
mixture move through the stationary phase at different speeds, causing them to separate
from each other. The nature of the mobile and stationary phases determines what moves
faster or slower, and how they are separated. This different migration time is called the
retention time. The distance travelled by each component between the point where the
original sample was added and the calculated distance from the solvent front is the retention
factor of each component present in the compound. Once the molecules are separated, the
Rf value can be used to identify the different components. The formula for calculating Rf is:
Rf = distance moved by the compound ÷ distance moved by the solvent.
There are 4 types of chromatography:
1. Paper chromatography: is an analytical method used to separate chemicals or
coloured substances. It was mainly used as a teaching tool, which was replaced by
other chromatographic methods, such as TLC.
2. Thin Layer Chromatography (TLC): is a technique in which compounds are separated
on a thin layer of absorbent material, usually a coating of silica gel on a glass or plastic
plate.
3. High Performance Liquid Chromatography (HPLC): is an analytical chemistry technique
used to separate, identify and quantify each component of a mixture. It relies on a
pump to pass a pressurized liquid solvent containing the sample mixture through a
column filled with solid adsorbent.
4. Gas chromatography (GC): is a common type of chromatography used in analytical
chemistry to separate and analyse compounds that can be vaporized without
decomposition. Typical applications of GC include testing the purity of a particular
substance or separating different components of a mixture.
Chromatography 2
Unit 2: Practical Scientific Procedures and Techniques
C: To classify components in mixtures, using chromatographic methods
Separate to identify
Ajmal Shekeb NOORMAL
, Unit 2C Ajmal Shekeb NOORMAL
Scenario
I'm a newly hired technical assistant at Chemcalequip, a big chemical plant. I must
demonstrate skills in a variety of practical procedures and techniques as part of my
induction period and in order to advance in my position. Identifying substances is a common
task for the firm.
I need to show that I can isolate and classify components in mixtures using various
chromatographic techniques. I'll need to clarify the techniques, analyse and assess my
performance, and make suggestions for changes in a report on the techniques I've used.
Chromatography is an analytical method used to separate coloured chemicals or substances.
Chromatography is used in industrial processes to: purify chemicals, test for trace number of
substances, separate compounds and test products for quality control. Capillary action is a
process in which liquid flows in a narrow space without the help of gravity or the opposing
external force. Liquids can be drawn between brush bristles, in thin tubes, in porous materials
such as sand and liquefied carbon fibre, or in biological cells. The intermolecular force
between the liquid and the surrounding solid surface triggers it. Different components of the
mixture move through the stationary phase at different speeds, causing them to separate
from each other. The nature of the mobile and stationary phases determines what moves
faster or slower, and how they are separated. This different migration time is called the
retention time. The distance travelled by each component between the point where the
original sample was added and the calculated distance from the solvent front is the retention
factor of each component present in the compound. Once the molecules are separated, the
Rf value can be used to identify the different components. The formula for calculating Rf is:
Rf = distance moved by the compound ÷ distance moved by the solvent.
There are 4 types of chromatography:
1. Paper chromatography: is an analytical method used to separate chemicals or
coloured substances. It was mainly used as a teaching tool, which was replaced by
other chromatographic methods, such as TLC.
2. Thin Layer Chromatography (TLC): is a technique in which compounds are separated
on a thin layer of absorbent material, usually a coating of silica gel on a glass or plastic
plate.
3. High Performance Liquid Chromatography (HPLC): is an analytical chemistry technique
used to separate, identify and quantify each component of a mixture. It relies on a
pump to pass a pressurized liquid solvent containing the sample mixture through a
column filled with solid adsorbent.
4. Gas chromatography (GC): is a common type of chromatography used in analytical
chemistry to separate and analyse compounds that can be vaporized without
decomposition. Typical applications of GC include testing the purity of a particular
substance or separating different components of a mixture.
Chromatography 2
