Consider that you wish to separate a mixture of histidine, serine and aspartate by ion exchange chromatography.
Using a cation exchange column at pH 5 , which amino acid would you expect to elute first and which last?
pKa and pI values are as follows:

Histidine: p K 1 = 1.82, p K 2 = 9.17, p K R = 6.00, pI = 7.59

Serine: p K 1 = 2.21, p K 2 = 9.15, pI = 5.68

Aspartate: p K 1 = 1.88, p K 2 = 9.60, p K R = 3.65, pI = 2.77

Question

Consider that you wish to separate a mixture of histidine, serine and aspartate by ion exchange chromatography. 
 Using a  cation exchange column at pH 5 , which amino acid would you expect to elute first and which last? 
 pKa and pI values are as follows: 
  
 Histidine:  p K 1  = 1.82, p K 2  = 9.17, p K R  = 6.00, pI = 7.59 
  
 Serine:  p K 1  = 2.21, p K 2  = 9.15, pI = 5.68 
  
 Aspartate:  p K 1  = 1.88, p K 2  = 9.60, p K R  = 3.65, pI = 2.77

Accepted Answer

Aspartate first. Histidine last.

Answer

Aspartate first. Serine last.

Answer

Histidine first. Serine last.

Answer

Histidine first. Aspartate last.

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Consider that you wish to separate a mixture of histidine, serine and aspartate ...

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