SDS-PAGE (Sodium Dodecyl Sulphate polyacrylamide gel electrophoresis) is an electrophoresis method that allows protein separation by mass. The gel acts as a sieve through which the proteins move in response to an electric field.
SDS-PAGE allows an estimation of the purity of protein samples and can also be used in confirming the presence of a particular protein in a sample through its molecular weight by running it simultaneously on the gel with another protein of known molecular weight, called the standard or protein ladder.
SDS is an anionic detergent and is used to denature the proteins. The negative charges on SDS destroy most of the secondary and tertiary structure of proteins and are strongly attracted toward the anode in an electric field. Because the charge-to-mass ratio is nearly the same among SDS-denatured proteins, the final separation of proteins is almost entirely dependent on the differences in relative molecular weight (MW) of polypeptides.