How does 2D electrophoresis separate proteins with identical molecular weights but different isoelectric points?

• A. By using a combination of hydrophobic interaction chromatography and SDS PAGE.
• B. By using SDS PAGE to separate based on molecular weights first, followed by isoelectric focusing.
• C. By using affinity chromatography followed by isoelectric focusing.
• D. By using isoelectric focusing to separate based on isoelectric points first, followed by SDS PAGE.

Answer: (D)