Proteins can be purified using techniques that involve electrophoresis, chromatography, ultracentrifugation, and other methods. You should understand the difference between electrophoresis with and without SDS, and know what SDS PAGE stands for. SDS PAGE is frequently used to obtain a quick estimate of a protein's molecular weight. Dialysis and gel filtration are separations on the basis of size. Gel filtration can produce good separations and can be used to estimate molecular weight if the protein is globular.
Affinity chromatography can be an extremely effective way to purify certain proteins.
Ion exchange is more useful with amino acids and peptides than with proteins, and gives a rather crude separation. There are several different modes of ultracentrifugation, used for different purposes. Equilibrium sedimentation is a time consuming and rigorous method for determining the molecular weight of a protein in non-denaturing conditions. This is important since most other molecular weight methods require that the protein be denatured. Once a protein has been purified, there are numerous methods for determining its properties.