Electrophoresis is an important separation method for proteins and nucleic acids. Electrophoresis enables separation of polyionic macromolecules by molecular weight, shape, secondary structure, and electric charge. For proteins, 5–20% polyacrylamide gels are almost universally used. The gels function both as anticonvective and as sieving media. The sieving properties are conveniently varied by varying gel composition. Because polyacrylamide gels absorb in the ultraviolet, direct absorbance measurements are rarely used. Instead, proteins or nucleic acids are detected and quantified by staining them with dye or colloidal metals.
Konan Peck and Michael D. Morris, "Thermo-Optic Behavior of Polyacrylamide Electrophoresis Gels," Appl. Spectrosc. 42, 513-515 (1988)