This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Classification and metabolism of amino acids, Subject name: Biochemistry
The ability of amino acids/proteins to behave like zwitterions forms the basis for separating them using the following technique 
Select and explain. 
A. Gel filtration chromatography, B. Ion exchange chromatography, C. Isoelectric focusing, D. Mass spectrometry
C: Isoelectric focusing
Answer: C: Isoelectric focusing 
Explanation: Isoelectric focusing is based on the isoelectric pH (pH at which a molecule carries no net charge). pH gradients created in the gel using polyampholytes. As there is no net charge, molecule stops moving during electrophoresis if they encounter their pI.