NuPAGE® LDS Sample Buffer (4X) (250 ml) is used to prepare protein samples for denaturing gel electrophoresis with the NuPAGE® gels. Optimal protein sample preparation for polyacrylamide gel electrophoresis (PAGE) requires denaturing and reducing the protein disulfide bonds. NuPAGE® LDS Sample Buffer contains lithium dodecyl sulfate at a pH of 8.4, which allows for maximal activity of the reducing agent.