Short Instructions - Amersham Pharmacia Biotech EPS 601 Manual Del Usuario

The parameter that should be chosen as the constant and thus control the electrophoresis depends on the
type of electrophoresis. In the case of homogeneous buffers throughout the system (same electrode and
gel buffer), the conductivity is constant during the electrophoresis. If the conductivity is constant, the
voltage will be proportional to the current and the power to the square of the current, according to (1)
and (2). This means that the result of the electrophoresis will be the same, regardless which parameter is
chosen for constant. For historical and practical reasons, voltage is most commonly used for regulation.
Submarine gel electrophoresis of DNA/RNA and pulsed field electrophoresis are usually run at constant
voltage. SDS-PAGE using continuous buffer systems is run at constant voltage or current.
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.

5.6 Short instructions

This section summarizes the main points covered earlier in this chapter. Use it as a check list once you
are familiar with the detailed programming and running instructions. Refer also to the separate
schematic operating guide included with the power supply. We recommend you keep this schematic
guide close by the instrument.
1. Turn mains power ON. The display should have the program number flashing.
2. Press ENTER for the actual program number, or use
Press. ENTER.
3. For each of the parameters Voltage, Current and Power, press
Confirm by pressing ENTER after each one, and the display will automatically move to the next
parameter.
4. Choose between manual break or automatic break. For automatic break, choose breakpoint units in
either Volthours (Vh) or time (h). Select the correct unit or, for manual break, choose "OFF" with
/ . Confirm with ENTER
5. If volthours or time were chosen, set the value to be used for the breakpoint with
6. If an automatic breakpoint was chosen under 4, you will be asked if you wish an alarm to sound at
the end of the run. Select YES or NO with
indicated by a small A as in "1A" to the right of the program number in the display.
7. When programming is completed, connect your electrophoresis unit to the outputs, and press RUN.
8. The actual voltage, current and power are shown on the display together with the elapsed time or
volthours (switch with
9. PAUSE CONTINUE can be used to interrupt and then continue the run.
10.The programmed parameters can be checked during the run by pressing SET.
11.The programmed run stops automatically or by pressing STOP
/ and press ENTER. If YES was chosen, this is
/ ).
EPS 601 - User Manual
/ to select the program number desired.
/ until the value desired is reached.
/ and ENTER.
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