Discontinuous gel electrophoresis process

In a discontinuous sodium dodecyl sulfate-polyacrylamide gel electrophoresis process for determining the molecular weight of a macromolecule by mixing the macromolecules with sodium dodecyl sulfate and tracking dye and adding the mixture to a support medium of polyacrylamide gel containing acrylamide monomers, placing the gel support medium in contact with an ion-containing buffer solution, subjecting the macromolecules and the support medium to a differential electricil potential to produce migration of the macromolecules, buffer ions and tracking dye, measuring the relative migration distance by the position of the tracking dye, and calculating the molecular weight of the macromolecule, the improvement which comprises using as the tracking dye a dye selected from the group consisting of thymol blue, phenol red, o-cresol red, orange G, m-cresol purple, and mixtures thereof.