How to Prepare a Sample for Gel Electrophoresis


Prepare the sample solution and the standard solution of known molecular weight.


Prepare a buffer solution with the nearest pH value to your sample.


Prepare the supporting medium (gel); common gel-forming materials are polyacrylamide, a water-soluble, cross-linked polymer, agarose and polysaccharide.


Place the gel between electrode compartments, with the bottom selected as anode or cathode, depending on whether anions or cations are being separated.


With a pipette, carefully drop a little amount of solution of each sample into one of several precast notches on top of the gel.


Add glycerol and a water-soluble tracking dye to the sample. The glycerol makes the sample solution dense, so that it does not mix into the buffer solution in the upper electrode chamber.

Tips and Warnings

  • The relative mobility of each component is calculated from the distance it has moved relative to the tracking dye.
  • When electrophoresis is carried out in a gel medium, the mobility is lower than would be expected because the gel exhibits a molecular sieving effect.
  • Electrophoretic separation is one of the most widely used methods in biochemistry. Although electrophoresis can be carried out freely in a solution, it is more convenient to use some kind of supporting medium. The two most commonly used supporting media are paper and gel. Gel electrophoresis is a technique much used with proteins and nucleic acids. DNA analysis is a significant case where gel electrophoresis is performed. DNA are polyelectrolytes that can be separated based on size alone.