Stacking Gel has a large pore size, which allows the proteins in the sample to move rapidly and concentrate or stack under the effect of the applied electric current. It is prepared in Tris-HCl buffer of pH 6.8. at this pH, glycine is predominantly in the zwitter ion form (pI = 5.4) and has the lowest mobility. Thus the SDS-protein complex get stacked in between the chloride ions (faster moving ions) and the glycinated ions (slowest moving ions).