Gel voltages and times

Nick Theodorakis nicholas_theodorakis at
Fri Feb 9 09:48:33 EST 2001

In article < at>,
  brookes at ("Paul S. Brookes.") wrote:
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> I have a real silly question about gel voltages.... Is the voltage you
> apply across them determined by the length, or the cross-sectional area?

The length. The voltage gradient drives the migration.

It used to be a practice to report electrophoresis runs as V/cm, so that
people could standardize the same gradient to the length of their set-up.

Anybody remember the fad for "King Kong" sequencing gels (of about 1.5-2
meters long, IIRC) back in the early '80s? ISTR they needed something
like 4000 V.

The cross-sectional area has nothing to do with the voltage gradient, but
the current (amps) will go up proportionally with the increase in cross-
section (or the number of gels attached to the power supply in parallel)
at a constant voltage.


Nick Theodorakis
nicholas_theodorakis at

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