The order of elution of AAs H, E, & K from a cation exchange column by a pH 6 buffer is
A) H E K
B) E H K
C) K H E
D) E K H

Question

Quizplus · Accepted Answer

At pH 6, histidine (H) is positively charged, glutamic acid (E) is negatively charged, and lysine (K) is positively charged. On a cation exchange column, negatively charged species elute first, followed by neutral (if any), and then positively charged species based on their affinity to the positively charged stationary phase. Since E is negatively charged, it elutes first, followed by H and K, which are positively charged. However, between H and K, H has a lower pKa and is less positively charged at pH 6, so it elutes before K.

The Order of Elution of AAs H, E, & K