Question

Explain the order of elution (with a buffer of pH 4) of the following pairs of amino acids through a column packed with Dowex 50 (Figure 21.3):

a. aspartate before serine c. valine before leucine

b. serine before alanine d. tyrosine before phenylalanine

Short answer

a. Aspartateelute first compared to serine

b. Serine elutes first compared to alanine

c. Valine elutes first compared to leucine

d. Tyrosine elutes first compared to phenylalanine

Step-by-step solution

Factors affecting order of elution

Cation exchange chromatography elutes amino acids based on their pI values.Amino acids with a negative charge does not bind with negatively charged resin instead they will repel and elute first. Amino acids with lowest pI value deliver first in the column because at a given=4 the net surface charge of amino acid will be negative. polar amino acids tend to elute first compared to nonpolar amino acids due to nonpolar resin coated in the column.

Order of elution

a. Aspartate is polar and serine nonpolar. Thus, aspartate elutes first.

b. Serine is polar and alanine nonpolar. Thus, serine elutes first.

c. Valine is polar and leucine nonpolar. Thus, valine elutes first.

Tyrosine is polar and phenylalanine nonpolar. Thus, tyrosine elutes first.