GE EPS 601 User Manual page 21

Operation 5
For discontinuous buffer systems, the resistance will increase as the electrophoresis
proceeds due to a decrease in conductivity. Running at constant voltage will result in
decreasing current and power. Constant voltage will thus be "safe" in the respect that
the power will not increase and produce more and more heat. On the other hand, the
separation will slow down and impair resolution due to an increased time available for
diffusion. Running at constant power would give a faster electrophoresis and controlled
power, while running at constant current would, at the first sight, seem to be problematic
because of increasing voltage and power.
During discontinuous electrophoresis, however, the voltage is not distributed evenly
across the gel. These gels have a region with low ionic strength that causes a high
electrical field strength. This region increases as the electrophoresis proceeds. This
means that the main part of the voltage is spread over a longer and longer distance
and a higher and higher power is tolerated. This is the reason why constant current is
chosen for such applications. It is, however, recommended to also limit the power as a
precaution against overheating the gel. The power supply will propably switch over to
limiting power at the end of the run due to increased voltage.
For detailed information about parameter values, always follow the gel supplier's
recommendations.
Electrophoresis Power Supply EPS 601 User Manual 18-1130-19 Edition AD 21