Which technique would be best to separate proteins based on their charge and size?

The technique that is best for separating proteins based on their charge and size is electrophoresis. This method utilizes an electric field to drive proteins through a gel matrix, allowing for separation according to their size and charge. In the process, smaller proteins move faster through the gel compared to larger ones, and proteins with different charges will migrate differently in the electric field, creating a distinct pattern based on both properties.

By manipulating the pH and the gel composition, researchers can optimize the separation, which is critical for analyzing proteins in various contexts, such as purifying enzymes, analyzing protein mixtures, or preparing samples for further analysis. This technique is foundational in many areas of biochemistry and molecular biology and is widely employed for protein characterization.

Other methods like immunodiffusion, Western blotting, and immunofixation each serve specialized purposes. For instance, immunodiffusion is primarily focused on antibody-antigen interactions, while Western blotting and immunofixation are used to detect specific proteins after they have been separated, often employing techniques like gel electrophoresis beforehand.