Chloride ions migrate as the leading ions, while glycine moves more slowly as the trailing ion. Their different migration behavior creates a moving boundary within the discontinuous buffer system. Proteins become compressed between these ion fronts into a narrow band before entering the resolving gel, reducing differences in their starting positions during SDS-PAGE.
The low-concentration stacking layer supports the initial compression of proteins into a narrow, aligned band before separation begins. The resolving gel then provides the phase in which proteins are separated. Maintaining this distinction helps proteins enter the resolving region from a similar position, which supports sharper bands and more reliable molecular-weight comparisons.
Acrylamide concentration, buffer composition, polymerization, and the boundary between the stacking and resolving gels are the critical preparation variables identified for this layer. If any of these features is poorly controlled, proteins may not be concentrated into a sufficiently narrow starting band. Careful control therefore supports consistent separation and clearer SDS-PAGE results.
The stacking gel and resolving gel serve sequential but different functions. The stacking layer concentrates proteins and aligns them before separation, whereas the resolving phase is where separation produces distinctions used for molecular-weight comparison. Preserving the transition between the two layers is important because the concentration step must precede the resolving phase to improve band sharpness.
Preparation requires making the low-concentration polyacrylamide layer, establishing the appropriate buffer composition, and controlling polymerization. The interface with the resolving gel must also be maintained carefully so that proteins can pass from the concentration phase into the separation phase. These steps determine whether samples enter the resolving gel as a narrow, consistent band.
The interface marks the transition from protein concentration to separation during SDS-PAGE. A properly controlled boundary allows the compressed sample to enter the resolving gel from a similar position, improving band sharpness and the consistency of molecular-weight comparisons. This is especially relevant when biological samples are compared across lanes and interpretation depends on distinct protein bands.