Contaminants in the sample such as high salt or urea lead to blurred bands or smiling gels in SDS-PAGE. With the ProtoGel Sample Prep Kit, interfering substances from upstream applications can no longer gain entry to the well. Contaminants are washed away with a simple method. The sample loaded contains only pure protein and loading buffer with no contaminants remaining to impede reproducible, high-resolution results. In addition to purification, proteins previously too dilute for SDS-PAGE can now be concentrated prior to electrophoresis with a simple method. The ProtoGel Sample Prep Kit concentrates proteins as dilute as 25ng/100