What is the purpose of chromatography? An amino add travels 72.5 mm up the chrom

Question

What is the purpose of chromatography? An amino add travels 72.5 mm up the chromatography paper while the solvent travels 90.9 mm. What is the Rrof this amino acid? What causes amino adds to travel up the chromatography paper different distances? What is the purpose of the ninhydrin? Why is it important in chromatography? Between the amino adds serine and alanine, which one would have the grater Rr with an isopropyl alcohol solvent? Use Intermolecular forces in your reasoning for this answer. isopropyl alcohol has the chemical formula C_3H_g0 and is very soluble in water. The molecule can be drawn as shown, below.

Explanation / Answer

Ans. 1. The purpose of chromatography is to- separate different components (pure molecules) of a mixture.

The separation technique depending on the relative polarity, mass, etc. of the components that enable their separation during chromatography experiment.

Ans 2. Rf value = Distance travelled by solute or amino acid / Distance travelled by solvent

Or, Rf value = 72.5 mm / 90.0 mm

                                    = 0.8055

Note: The distance is always measured from baseline. Rf value always lies between 0-1.

Ans. 3. I. The relative solubility of the amino acids in the mobile phase, and II. their polarity determine the movement (travelling up) of amino acids.

In paper chromatography, the molecule with greater polarity moves slowly and the one with low polarity (i.e. non-polar) moves faster along with the solvent.   

Cellulose is a polar molecule. It has higher affinity for polar molecules and retard their movement. However, the non-polar solutes exhibit very low affinity for cellulose paper and higher affinity for non-polar mobile phase. So, they move faster dissolved in the solvent without being retarded by cellulose.

Ans. 4. The purpose of ninhydrin is to detect the amino acids separated during paper chromatography.

Ninhydrin stains amino acid spots in brown or purple, which otherwise would be invisible. When the paper is sprayed with ninhydrin, all the spots containing amino acids (say, different amino acids) become visible as brown or purple spots. The distance of each spot from the base line is used to calculate the Rf value and characterize the type of amino acid present in mixture.

Ans. 5.   Paper chromatography

Solvent = Isopropyl alcohol CH3CHOHCH3. That is, the solvent is more non-polar (has bulky   aliphatic chain, (CH3CHOHCH3).) that it is polar (a single -OH group).   

            Amino acids = Serine (polar amino acid), Alanine (aliphatic, non-polar amino acid)

Being polar, serine has higher affinity for polar cellulose paper. So, serine retains (holds) on the cellulose paper relatively strongly because both have same polarity. The solvent, isopropanol, is polar because of having -OH group. Therefore, serine also shows solubility in the solvent.

Alanine is non-polar and does not shows affinity for cellulose paper, so does not get retained on paper. Isopropanol is also a good non-polar solvent because it has bulky aliphatic group. So, alanine also shows considerable solubility in the solvent.

Now, Note:

            A. Serine: has affinity for cellulose (retards its movement)

                            Shows solubility in the solvent

            B. Alanine: has NO affinity for cellulose (does NOT retards its movement)

                            Shows greater solubility (solvent is more non-polar than being polar) in the solvent

Therefore, alanine moves faster than serine in paper chromatography because it has less polar than serine.

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.