Unit 2- Practical Scientific Procedures and Techniques
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name, Unit 2 LA C Separate to identify
Aim and introduction:
In this report, in my role as a I am going to undertake chromatographic techniques
to identify components in chemical mixtures.
Chromatography is a technique for separating chemical mixtures in preparation for
analysis. It helps to separate mixtures “according to their solubility in the mobile
phase and their absorbance to the stationary phase”(Explain how chromatography is used to
separate components in a mixture. | MyTutor, 2021). “The mobile phase is the part of the
chromatography setup that moves and the stationary wave is the part of the set up
that does not move”(Explain how chromatography is used to separate components in a mixture. | MyTutor, 2021).
“Components that are more soluble in the mobile phase will travel faster because
there are fewer interactions with the stationary phase to slow down” (Explain how
chromatography is used to separate components in a mixture. | MyTutor, 2021) the movement of the
component. The main types of chromatography are:
● Paper chromatography
● Thin layer chromatography (TLC)
● Gas chromatography (GC)
● High performance liquid chromatography (HPLC)
● Column chromatography
● Ion-exchange chromatography
● Gel-permeation (molecular sieve) chromatography
● Affinity chromatography
● Dye-ligand chromatography
● Hydrophobic interaction chromatography
● Pseudo Affinity chromatography
Principles of chromatography:
Chromatography works on the principle that molecules in a chemical mixture
applied to a surface or into a solid, as well as a fluid stationary phase (pigment),
separate while moving with the help of a mobile phase (solvent). Molecular
properties related to adsorption (liquid to solid), partition (liquid to solid), and affinity
(differences in molecular weights) are all important elements in this process. “Some
components of the mixture linger longer in the stationary phase and move slowly
through the chromatographic system as a result of these differences, while others
flow quickly into the mobile phase and leave the system faster”(Coskun, O., 2016).” The
basic component effective in the separation of molecules from each other is the
type of interaction between the stationary phase, mobile phase, and substances
contained in the mixture”(Coskun, O., 2016).
Part C.P6
1
, name, Unit 2 LA C Separate to identify
Solubility of paper chromatography and TLC:
Solubility has little effect on chromatography; nevertheless, changes in
intermolecular forces can alter chromatography. The solubility of an analyte is a
prerequisite for selecting a mobile phase in chromatography. The components
must be solvent-soluble and unaffected by the solvent. Some compounds are
more soluble in certain solvents than others. The compounds that do not dissolve
are the ones that do not move, whereas the ones that dissolve the most are the
ones that move the most.
The bonds that form between one substance and a surface are explained by
adsorption. Because the compounds are constantly moving between the
stationary and mobile phases, these bonds are not permanent.
The compounds in chromatography can only move when they are in the mobile
phase, or when they are dissolved in the solvent. When adsorption to the surface
occurs, the solvent is temporarily halted, yet the solvent continues to travel. To
summarise, the more powerful a substance is, the shorter the distance it can go up
the chromatography paper.
Pigments are adsorbed onto the surface of solid particles or fibres in a solid
stationary phase. Separation occurs due to the relative forces of attraction
between the stationary phase, the mobile phase, and the pigment.
“Polar solutes dissolve in polar solvents, while nonpolar solutes dissolve in nonpolar
solvents” (Solubility Factors When Choosing a Solvent, 2021). It's critical to determine if the test sample
is polar or nonpolar before choosing a solvent that will allow it to dissolve easily in
chromatography.
“As the solvent soaks up the plate, it dissolves the compounds in the spot where
the” (A. Introducing Chromatography: Thin Layer Chromatography, 2021) baseline has been placed first. As
the solvent moves upwards, the component that is present will be carried up the
chromatography paper.
The speed with which the compounds are transported up the chromatography
paper is determined by two factors:
● The degree to which the component is soluble in the solvent: this will be
determined by the degree of attraction between the compound's
molecules and those of the solvent.
● The amount of the substance that absorbs to the stationary phase: the
amount of attraction between the compound's molecules and the silica gel
will determine this.
So in conclusion, “adsorption is not permanent; a molecule moves back and forth
between being adsorbed on the silica gel surface and being dissolved in the
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