Hoefer SE400 - Manual (Page 28)

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2.5 Resolving the sample
Electrophoresis parameters for discontinuous
polyacrylamide gels
Gels may be run at either constant current or
constant voltage settings. A constant current
setting is traditionally used with a discontinuous
buffer system so that the rate of electrophoretic
migration remains unchanged throughout the
run. Under constant current conditions, the
voltage increases as the run proceeds. A lower
current setting is recommended for higher reso-
lution. The optimal current level must be deter-
mined empirically; the main factors that must be
balanced are the gel concentration and migration
speed, and the resulting Joule heating and band
distortion. Table 3 lists starting point guidelines
and adjustments for gel thickness, number of
gels, and migration rate.
Table 3. Laemmli buffer system starting point guidelines
Gel thickness* 1.5 mm
Current per gel † 25 mA constant current
Starting voltage 80–90 V
Gel length (cm) model final voltage (V)
16 SE400 200–250
24 SE410 275–325
* Thicker or thinner gels require proportionally more or less
current. For example, a 0.75 mm gel, which is half as thick
as a 1.5 mm gel, requires half as much current, or 12.5 mA.
† The current must be multiplied by the number of gels. For
instance, if a 1 mm 2-gel sandwich is installed, twice as
much current is required than for a single 1 mm gel at the
same voltage.
Note: The cross section
(and current requirement) is
determined by gel thickness.
The running time is determined
by the length of the plate.