For each pair of amino acids listed below, predict which one would be first to elute from a cation-exchange column. Assume the buffer pH begins at 3.25 and is increased in a stepwise fashion to pH 6.
a) Asp, Glu d) Lys, Phe
b) Ser, Val e) Leu, Val
c) Phe, Ala f) Gly, Ala