Unit 2C | Separate to Identify | RESUB Practical date: 30/11/23
Paper Chromatography of Plant Pigments
Identification of Plant Pigments, Practical 1
Aims:
The aim of this practical was to investigate pigments present in leaves using
paper chromatography.
Introduction:
Plants contain an organelle called chloroplast. Within chloroplast is the
pigment chlorophyll, the main pigment that absorbs light during
photosynthesis. However, there are other photosynthetic pigments within a
plant which try and absorb many different wavelengths of light so they can
maximise the rate of photosynthesis.
The different pigments are:
▪ Chlorophyll a
▪ Chlorophyll b
▪ Xanthophyll
▪ Carotene
▪ Pheophytin
Despite the different pigments, none of them absorb the green region of the
light wavelength so they reflect it hence why the plant appears green.
Where in the structure of chloroplast are the different pigments found?
Chlorophyll a and chlorophyll b are found in the thylakoid membranes of
chloroplast. Xanthophyll’s and carotenes are part of the carotenoid family.
They are both found in the proteins and membranes of chloroplast. I (Panawala,
Lakna 2017)
How does paper chromatography work?
The way it functions is by using the components' differential partitioning of
compounds between a stationary phase (the paper) and a mobile phase (the
solvent). The mixture's components separate into discrete bands or spots on
the paper as a result of the solvent carrying the mixture's constituents up the
paper strip. The compounds in the mixture have unique strengths of attraction
, Unit 2C | Separate to Identify | RESUB Practical date: 30/11/23
towards the stationary phase and the mobile phase which causes them to
move at different rates up the chromatogram. II (Study Mind, n.d.) | III (Sciencedirect.com, 2014)
| IV (oakesrl1, 2010)
Small amounts of the sample are spotted onto the filter paper (the stationary
phase) along the origin line (a line drawn faintly in pencil towards the bottom
of the paper). The paper is then placed into a non-aqueous organic solvent (the
mobile phase). As the solvent moves along the paper, the components are
carried along with it as it dissolves. The different components within the
sample have unique affinities for the solvent and the paper. They differ in
solubility, molecular mass and type of bond hence why each component within
the sample travel at different rates. The size of the molecules itself also affect
the rate of its movement so the larger molecules will move slower than the
smaller molecules.
The more soluble the component is, the quicker and further it travels. This is
due to the fact that some molecules are selectively adsorbed (attracted/stick
to the paper) because the filter paper itself contains tiny water molecules
between the cellulose fibers-which absorbs moisture from the air. The amount
of adsorption depends on the chemical properties of the molecule, the polarity
and the solvent that is used.
Certain molecules may have a stronger affinity towards the paper due to the
hydrogen bonding whereas other molecules may dissolve in the solvent. The
less soluble a component is, the slower and less distance it will travel.
Paper Chromatography of Plant Pigments
Identification of Plant Pigments, Practical 1
Aims:
The aim of this practical was to investigate pigments present in leaves using
paper chromatography.
Introduction:
Plants contain an organelle called chloroplast. Within chloroplast is the
pigment chlorophyll, the main pigment that absorbs light during
photosynthesis. However, there are other photosynthetic pigments within a
plant which try and absorb many different wavelengths of light so they can
maximise the rate of photosynthesis.
The different pigments are:
▪ Chlorophyll a
▪ Chlorophyll b
▪ Xanthophyll
▪ Carotene
▪ Pheophytin
Despite the different pigments, none of them absorb the green region of the
light wavelength so they reflect it hence why the plant appears green.
Where in the structure of chloroplast are the different pigments found?
Chlorophyll a and chlorophyll b are found in the thylakoid membranes of
chloroplast. Xanthophyll’s and carotenes are part of the carotenoid family.
They are both found in the proteins and membranes of chloroplast. I (Panawala,
Lakna 2017)
How does paper chromatography work?
The way it functions is by using the components' differential partitioning of
compounds between a stationary phase (the paper) and a mobile phase (the
solvent). The mixture's components separate into discrete bands or spots on
the paper as a result of the solvent carrying the mixture's constituents up the
paper strip. The compounds in the mixture have unique strengths of attraction
, Unit 2C | Separate to Identify | RESUB Practical date: 30/11/23
towards the stationary phase and the mobile phase which causes them to
move at different rates up the chromatogram. II (Study Mind, n.d.) | III (Sciencedirect.com, 2014)
| IV (oakesrl1, 2010)
Small amounts of the sample are spotted onto the filter paper (the stationary
phase) along the origin line (a line drawn faintly in pencil towards the bottom
of the paper). The paper is then placed into a non-aqueous organic solvent (the
mobile phase). As the solvent moves along the paper, the components are
carried along with it as it dissolves. The different components within the
sample have unique affinities for the solvent and the paper. They differ in
solubility, molecular mass and type of bond hence why each component within
the sample travel at different rates. The size of the molecules itself also affect
the rate of its movement so the larger molecules will move slower than the
smaller molecules.
The more soluble the component is, the quicker and further it travels. This is
due to the fact that some molecules are selectively adsorbed (attracted/stick
to the paper) because the filter paper itself contains tiny water molecules
between the cellulose fibers-which absorbs moisture from the air. The amount
of adsorption depends on the chemical properties of the molecule, the polarity
and the solvent that is used.
Certain molecules may have a stronger affinity towards the paper due to the
hydrogen bonding whereas other molecules may dissolve in the solvent. The
less soluble a component is, the slower and less distance it will travel.
