Proteins are separated on the basis of size by

The most widely used method for determining the purity of a protein is SDS - PAGE - Poly-acryl-amide gel-electrophoresis (PAGE) in the presence of the anionic detergent sodium dodecyl sulfate (SDS). Electrophoresis separates charged bio-molecules based on the rates at which they migrate in an applied electrical field.Since the charge-to-mass ratio of each SDS polypeptide complex is approximately equal, the physical resistance each peptide encounters as it moves through the acrylamide matrix determines the rate of migration. Since large complexes encounter greater resistance, polypeptides separate based on their relative molecular mass (M), Individual polypeptides trapped in the acrylamide gel are visualized by staining with dyes such as Coomassie blue.Ref: Harper 28th Ed. Page-23, Harper 27th Ed. Page: 24