Technical methods SUPPORTING MEDIA AND APPARATUS Electrophoresis using a constant potential across the separation field

Reproducibility of electrophoretic runs depends on the maintenance of a smooth and constant voltage gradient within the supporting medium or separation chamber. Power packs to supply constant current or constant voltage as measured at the pack are readily available, but if such a pack is used with constant voltage, the proportion of the voltage drop available for the electrophoretic separation will be affected not only by changes in the resistance in the separation field, but also by changes in the external circuit, which will be certain to occur at the electrodes, separation membranes, or buffer reservoirs. For this reason, it is usual to work with constant current, since the voltage drop in the separation field will then be independent of the resistance changes in the external circuit