Chem Lab Report (Paper Chromatography)

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Daswani 6A (23)

Experiment 20

Paper Chromatography

Objective
           To illustrate the use of paper chromatography for the separation and identification of amino acids.


Results

Special Questions
1.> For each amino acid, compare your two Rf values with each other and with the specimen results
      Why do you think there is some variation?

 Both Rf values are the same for aspartic acid but there is some variation for leusine & lysine. This may due to:
            1.> The grease on our fingers contaminated on chromatographic paper will affect greatly on the amino acids that are less
                   polar.
            2.> The measurement error of the distance travelled by solvent and/or amino acid.
            3.> The shape of chromatographic paper is not exactly square-shaped, so that one side of the paper may be lifted and the
                   speed of the solvent travel in one side is faster.
            4.> The different proportion of chemicals (
∵measured by measuring cylinder) may be used between the researchers and us, and
                   the temperatures may also different, thus R
f values obtained are different.

2.> Why do Rf values change when a different solvent is used?
 Each amino acid has different polarity and each solvent has different polarity, too. So, when a different solvent is used, amino
            acids will travel at a different speed.
            For example, if a more  polar solvent is used, the more polar amino acid will travel at a faster speed
            and has a larger R
f value.
            On the contrary, if a less polar solvent is used, the non-polar amino acid will travel faster and the slowest one should be the
            polar amino acid.

3.> Why is it so important to avoid touching the chromatographic paper with your fingers?
 There are some secretion on our fingers - amino acids and grease.
            Amino acids on our fingers will result in the unexpected colour zone appears on chromatographic paper after spraying
            ninhydrin solution. This will make us confused and more difficult to obtain the appropriate R
f values.
            Grease on our fingers will affect non-polar amino acids most, since they are more likely to dissolve in grease than more polar
            developing solvent, they will move at a higher speed. Hence the R
f values are affected.
            Moreover, there may have some chemicals on our fingers, e.g. ammonia, water, etc. These will affect the polarity of the
            developing solvent and thus the R
f values. 

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Precaution
          1.> Small area with concentrated spot of amino acid should be applied to obtain a deeper colour of spots.
          2.> The edges of chromatographic paper should not touch the sides of the beaker since he solution at edges will move faster due to capillary action.
                The spots will bend and R
f value is affected.
          3.> The beaker should be saturated with the solvent before putting the chromatographic paper in. If the atmosphere is not saturated, there is a
                diffusion gradient between chromatographic paper and air, some solvent may vapourize from chromatogram and results in long tail of spots.
          4.> ...

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