SDS-PAGE is the acronym for "Sodium dodecyl sulfate polyacrylamide gel electrophoresis", a laboratory method used to separate proteins. In the term disk electrophoresis, "disk" stands for "discontinuous".
Sodium dodecyl sulfate (SDS) is added to the sample material to be examined. SDS is deposited on the proteins and unfolds them. This gives them a strong negative charge. This covers the intrinsic charge. SDS binds to the amino acid chain in a stable ratio so that the charge of the molecule is proportional to its mass.
After further preparation processes, electrophoretic separation takes place in a polyacrylamide gel. The migration rate in the gel depends on the size of the molecule. The smaller a protein, the faster it migrates in the gel. The walking distance is inversely proportional to the logarithm of the molecular mass.