How can you separate proteins from water?

Answer 1

The easiest way to separate proteins from bulk water is by using ultra-centrifugation. The "ultra" only means that these centrifuges are capable of applying a much greater force on a sample by spinning at a faster rotational velocity and/or by having a longer radius (or lever).

Another method that is used, especially if there are fewer than some critical number of different proteins in a solution or suspension, is [gel] electrophoresis. In this method, which is also the one typically used to separate differently sized pieces of DNA, the protein solution or suspension is placed in a small well inside of a rectangular container containing a gelatinous material. A DC voltage is then applied across the two ends of the container. Because of their large size, proteins easily acquire an electrical charge. Proteins of different sizes and having different charges migrate through the gel at different rates when the voltage is applied, thus separating the different proteins (or pieces of DNA).