At physiological pH, carboxy terminal of peptide is
In ion-exchange chromatography, proteins interact with the stationary phase by charge-charge interactions. Proteins with a net positive charge at a given pH will tightly adhere to beads with negatively charged functional groups such as carboxylates or sulfates (cation exchangers).
 
Harper, Ed 30, Pg 27
Positive charged
Negative charged
Neutral
Infinitely charged