Explain how amino acids could be identified using gel electrophoresis

The sample of amino acids is placed in the center of a polyacrylamide gel, across which a voltage is applied. Depending on the pH of the buffer, the amino acids will move at different rates towards either the positive or negative electrodes . Amino acids will stop moving once they have reached their isoelectric point- the pH at which amino acids have no overall charge. When separation is complete, the amino acids are sprayed with ninhydrin and can be identified by comparing the distance traveled with known standards.