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# Analysis of amino acids by chromatography on paper

A mixture of amino acids can be separated by chromatography on paper. Contrary to the →       chromatography of an ink stain the amino acids are not colored. It is necessary to reveal their position with ninhydrin after drying . In principle, the more polar amino acids are retained more on paper by making H-bonds with cellulose and will thus be taken along slower by the solvent:

3 is more polar than 2 which is more polar than 1 !

Comparison method

1 is the mixture of amino acids to be analyzed, 2,3,4,5 are pure amino acids which are used for comparison. The experiment shows that 1 is a mixture of 2,4 and 5, but does not include 3!

$R_f$ value method After the chromatography, the distance $d_{solv}$ between the front reached by the solvent and the level of the solvent in the tank as well as the distances $d_1, \; d_2$ between the different spots and this level are measured.

We calculate: $R_{f1}=\frac{d_1}{d_{solv}}$ $R_{f2}=\frac{d_2}{d_{solv}}$ These values are characteristic for amino acids on a given support with a given solvent and make it possible to identify them, for instance: