For each of the following separations, should a cation-exchange or anion-exchang
ID: 521506 • Letter: F
Question
For each of the following separations, should a cation-exchange or anion-exchange column be used? A mixture of I^-, F^-, NO^-_3, SO^2-_4, and Cl^-. anion-exchange column not enough information cation-exchange column A mixture of Na^+, K^+, Ca^2+, Mg^2+, and Ba^2+. not enough information cation-exchange column anion-exchange column A mixture of amino acids under basic conditions, where the pH is greater than the pl of the amino acid. anion-exchange column not enough information cation-exchange columnExplanation / Answer
Case 1: All are anions (negative ions), therefore, anion-exchange column is required to be used. In anion exchange column, anions are retained since the stationary phase has positive functional group. The ion strength of those positive functional groups on resin (stationary phase) can be adjusted to effect on the anion binding and hence the retention time by shifting the ion-exchange equilibrium position.
Case 2: All are cations (positive ions), therefore, cation-exchange column is required to be used. In cation exchange column, cations are retained since the stationary phase has negative functional group. The ion strength of those negative functional groups on resin (stationary phase) can be adjusted to effect on the cation binding and hence the retention time by shifting the ion-exchage equilibrium position.
Case 3: Anion-exchange column is required. pH>pI indicates that in basic conditions, the acid functional group of amino acids will be deprotonated as, [R'CH(NH2)COO-]. Thus, it will behave as anion. Therefore, anion exchange column can be used following the previous criteria (Case 1).
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