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Pearson BTEC Level 3 Applied Science Assignment 2C: Chromatography
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This is a distinction example for the unit of 2C: Chromatography and should be used as a guide only and not to be copied.
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Assignment 2C: ChromatographyNAME: ___________________________
I certify that the work submitted for this assignment
is my own. I have referenced any sources used in the
work. I understand that a false declaration is a form
of malpractice.
DATE: ________________
, Introduction
Chromatography has two main objectives of separating and identifying a mixture in order to analyse a
substance and to calculate an Rf value to compare or create published data (Coskun, 2016). The
compounds are a result of the successful separation of the mixture on the chromatogram but are also
found within the solvent as the mobile phase, with the stationary phase being the phase in which the
solvent travels through via capillary action, and the mobile phase becoming the solvent after entering
the stationary phase. In the two experiments completed the 1st experiment used chromatography paper
as the stationary phase, with the 2nd experiment using Thin Layer Chromatography (TLC) with a silica gel
coating. The solvent in the 1st experiment was a mixture of propane and petroleum spirit with the 2nd
experiment using propane, petroleum spirit and cyclohexane, these are put into a development
chamber with a wick to allow for the saturation of the atmosphere in the chamber with the evaporated
solution. The chromatograph is the final piece after the mobile phase has reached the solvent front.
Solvents can have different polarities and molecular masses which can affect the distance travelled on
the stationary phase depending on the material of the stationary phase, differential partitioning is the
different attraction compounds may have to the stationary phase than others, which is due to the
attraction of intermolecular forces between compounds and the stationary phase, which reduces
movement up the chromatogram. It is most common to use a very polar stationary phase such as silica
gel to complete chromatography as they contain hydroxyl groups which have hydrogen bonds (the
strongest type of intermolecular force) in them, meaning compounds that are non-polar are measured
to be nearer to the solvent front which is where the mobile phase stops on the stationary phase and
compounds that are polar are measured to be nearer to the base line which is where the specimen for
the separation is placed.
A Rf value or retention factor can be calculated using the following equation:
distance moved by compound
Rf =
distance moved by mobile phase
This then allows for comparable figures with published data to determine the name of the compound
and the components on the chromatogram, to determine what makes up a specific mixture.
Paper chromatography is usually used in an educational setting as a cheap and safe alternative to a
method such as TLC, a common experiment would be to separate food dye using distilled water as the
solvent, as is taught in the GCSE syllabus. Thin Layer Chromatography involves a silica gel coating in
order to aid adsorption through its polar bonds from the chemical structure of Si-O-H, we can view the
bonds present as dipole-dipole as well as the O-H bond signifying the presence of hydrogen bonds.
Another type of chromatography that can be used is gel permeation which is the size separation of
molecules in a column with their pore size known. Compounds that contain molecules of a larger size
that are unable to pass through the pores elute or are removed faster. This process is used in industry to
remove fats in the analysis of pesticides for fatty samples. (Arsalan & Younus, 2018)
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