2. Assume that the edges of chromatographic paper are not touch the sides of the beaker since the solution at edges will move faster due to capillary action. The spots will bend and Rf value is affected
3. Assume that the beaker is saturated with the solvent before putting the chromatographic paper inside. As the atmosphere is not saturated, there is a
diffusion gradient between chromatographic paper and air, some solvent may vapourize from chromatogram and result in long tail of spots.
4. Assume that the temperature remains constant, as the temperature may affect Rf values.
Errors
- The origin line should not marked by the ball pen, since the ink will dissolve in the developing solvent and the line fades gradually or even an additional spot can be observed.
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Ninhydrin solution should not spray too much on paper since it will blur and spreads the coloured spots. It's because the solvent that are used to dissolve ninhydrin can also dissolve amino acids.
- There are some secretion on our fingers, for example amino acids and grease. It may result in the unexpected colour zone appears on chromatographic paper after spraying ninhydrin solution.
- The shape of chromatographic paper may not exactly be the square-shaped, so that one side of the paper may be lifted and the speed of the solvent travel in one side is faster.
- The diameter of capillary tubes may not exactly the same, so the proportions of the amino acids obtained by the capillary tubes may not the same, and the colour may not be seen clearly.
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The spots are too large, so it is hard to identify the center of the spots
Improvements
1. The origin line should be marked by pencil. Since, the pencil is made of Carbon, and that will not undergo the chromatography test and not dominate the effect on that solvent in the paper.
2. Wear the gloves are necessary during the experiment in order to prevent the grease or amino acids on our fingers will contaminate the chromatographic paper and affect the accuracy of the experiment.
3. Use the smoothest side to be the starting point to ensure the solvent travel in on average.
4. Repeat the step of placing a small amount of amino acids in paper more than 10 times to make sure the spots will be present for good visual observation when the paper is developed.
Conclusion:
The paper chromatography did show that the unknown B could be defined to aspartic acid and tyrosine. By the chromatographic paper, the unknown B contains both deep blue and purple colour, and it matches the deep blue of aspartic acid. And the shape of the unknown B is teeth-shape, which is same as the tyrosine. So, the unknown B is made of aspartic acid and tyrosine.
