Size-exclusion chromatography (SEC).  In this method, proteins in solution are separated on the basis of size.  A solution is placed on top of a gel column and allowed to move down the column.  A typical gel is composed of small polymeric beads with pores of varying size.  As the solution flows through the gel column smaller proteins can enter the pores of the beads and are retarded while the larger proteins do not enter the pores and thus are eluted faster.

SDS-PAGE. Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis is another method used to separate proteins depending on their size.  SDS is a detergent that can coat proteins evenly, resulting in a uniform negative charge to mass ratio.  Proteins in an SDS solution are placed on a polyacrylamide gel which is equilibrated with a buffer.  A voltage is applied across the gel and the negatively charged SDS-coated proteins migrate through the gel toward the positive electrode.  Larger proteins migrate more slowly in the gel then do smaller proteins.  The advantage of this method is its high resolving power to separate proteins that differ only slightly in mass.

Electron microscopy. This method uses a beam of electrons that is focused on a target and which produces an image of it that cane be magnified approximately two million times greater than an ordinary light microscope.

X-ray Crystallography. An analytical technique that uses x-ray diffraction by a protein crystal to permit deduction of the 3D structure of a protein.  A protein crystal is bombarded with x-rays, producing an x-ray diffraction pattern that can be translated into an electron density map and eventually into a model showing the 3-dimentional arrangement of atoms in the protein crystal.