Used in SDS-PAGE (sodium dodecyl sulfate–polyacrylamide gel electrophoresis) to prepare protein samples for separation by molecular weight. It denatures proteins by breaking disulfide bonds and coating them with negative charge, ensuring uniform charge-to-mass ratio. This allows proteins to migrate through the gel based solely on size. Contains SDS, a reducing agent (like β-mercaptoethanol or DTT), and a tracking dye (e.g., bromophenol blue) to monitor electrophoresis progress. Also includes glycerol to increase sample density, helping it settle into wells during loading. Commonly heated with samples before gel loading to ensure complete denaturation.