Which method allows for the separation of molecules based on their size?

• A. Isoelectric focusing
• B. Gel filtration chromatography
• C. Affinity chromatography
• D. Liquid chromatography

Answer: (B)

The method that allows for the separation of molecules based on their size is gel filtration chromatography. This technique utilizes a porous gel matrix that creates a labyrinth for molecules as they pass through. Larger molecules are unable to enter the smaller pores of the gel and therefore move through the column more rapidly, while smaller molecules can enter the pores and take longer to navigate through the gel. Consequently, this results in a size-based separation, where larger molecules elute first from the column and smaller molecules follow.

Other methods, while effective for their specific purposes, do not primarily focus on size. Isoelectric focusing separates proteins based on their isoelectric point, which is influenced by the pH of the environment, rather than their size. Affinity chromatography relies on specific binding interactions between a target molecule and a ligand attached to the column, making it useful for purifying specific substances but not for separating based on size. Liquid chromatography can separate a variety of compounds based on several factors, including size, but it is not exclusively focused on size as gel filtration chromatography is.