Paper Chromatography Lab Report

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Biology Report 6 Name : Tan Mei Jing Student No. : 2017141025 Subject : Paper Chromatography Group : 2 Date of Experiment : 31/10/2017 Date of Submission : 2/11/2017 Objectives To understand the principle and mechanism of paper chromatography. To investigate (and separate) the different pigments present in lettuce leaves by using the paper chromatography technique. Hypothesis Lettuce contains mostly chlorophylls (both α and β) for the green color. Results Pigment Distance Travelled (cm) Rf Value Chlorophyll α 6.2 6.2/7.2=0.86 Chlorophyll β 5.3 5.3/7.2=0.74 Unfortunately, our chromatogram as shown in the photo attached, does not reveal any traces or colors of carotene (orange) and xanthophyll…show more content…
It provides a measure of how far a chemical can travel in response to the solvent movement. The closer is the Rf value to 1, the more soluble is the pigment in that solvent, and thus the further upwards will its spot move. The Rf value is unique for the same material (solute; pigment), and this serves as a standard for us to identify unknown substances. Further tests subsequent to paper chromatography such as absorbance test can be performed to more accurately determine the identity of each constituent. The supernatant that contains the leaf pigments separates into different colors because these pigments absorb specific wavelengths of visible light during photosynthesis. Chlorophylls absorb red and blue light and reflect green light, which is why we see the chlorophylls as green color. Carotenes and xanthophylls absorb violet, blue and green light and reflect red and yellow light, which gives them the orange or yellow color. Despite red, orange and yellow pigments are present, we normally see leaves as green in color because the quantity of these pigments might be smaller, and the abundance of green chlorophyll masked their colors. The factors that affect the Rf value…show more content…
By grinding, we provide the mechanical disruption that force open (damage) the cell wall so that the contents we are interested in (pigments) will spill. Adding acetone while grinding the leaves allows the dissolution of pigments, which is useful for first-step separation of pigments from cell debris via centrifugation. The principle of paper chromatography is as below: Paper chromatography is a type of partition technique utlising the difference in polarity of each pigment and their limit of affinity to both the mobile and stationary phase. Essentially, the molecular structure of paper is the base that paper chromatography can work. Noticing that paper is made up of cellulose fibers, which are polymers with hanging –OH groups that causes polar (water) molecules to adsorb to (by forming hydrogen bonds or dipole-dipole interactions). This makes up the stationary phase (paper), and the mobile phase (solvent). After soaking the bottom part of the paper into the our petroleum ether & acetone solvent, the solvent front will travel up the paper because it has little affinity (mainly nonpolar) to the polar stationary
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