constant voltage or amperage

Nick C.K. Heng xenofobe at
Sat Sep 13 03:53:40 EST 1997

On Thu, 11 Sep 1997 14:54:01 -0600, kirkpat at (Rob
Kirkpatrick) wrote:

>We had a "discussion" in the lab yesterday about whether to use constant
>voltage or constant amperage when running an acrylamide gel (protein or
>DNA).  We decided constant amperage was better in all cases but our
>arguments were weak.  Does anyone out there actually prefer one or the

I've always thought that voltage was the "driving force" behind the
migration of DNA in the agarose. Amperage was the determinant of the
temperature. If the temp. got too hot, the bands would look funny
after staining.
In my experience, the TBE buffer from the same bottle can vary in
voltage depending on the ambient temperature. I know in summer the
voltage is lower, thus the gels run slower. I usually run the gel at
50 mA constant current to keep the temperature at an acceptable limit.
The voltage starts at about 82V and drops to about 65V over time. We
use the Pharmacia GNA-100 apparatus.

My personal preference: it would be constant voltage but due to the
effect of the ambient temperature, I'm "forced" to run at constant
amperage. However, it all boils down to how far your dye front runs
regardless of the run parameters... and whether the bands you want to
see are actually there! :)

Kind regards,

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