The ionic strength discontinuity between the loose stacking gel and the hard running
gel leads to a voltage discontinuity as current is applied. The goal of these gels is to
maximize resolution of protein molecules by reducing and concentrating the sample to
an ultrathin zone (1-100 nm) at the stacking gel:running gel boundary. The protein
sample is applied in a well within the stacking gel as a rather long liquid column (0.2-
0.5 cm) depending on the amount and the thickness of the gel or tube. The protein
sample contains glycerol or sucrose so that it can be overlaid with a running buffer. This
buffer is called the running buffer, and the arrangement is such that the top and bottom
of the gel are in running buffer to make a circuit.