Anion exchange resins will bind to negatively charged molecules, displacing the counter-ion.
Second, the pH of the solution can be gradually decreased which results in a more positive charge on the protein, releasing it from the resin.
Both of these techniques can displace the negatively charged protein which is then eluted into test tubes fractions with the buffer.
Composition of ionizable side chain groups will determine the total charge of the protein at a particular pH.
If the pH is above the pI, the protein will have a negative charge and bind to the matrix in an anion exchange column.