Help, decreasing temp. during long sequencing runs!

Jeff Lawrence lawrence at bioscience.utah.edu
Thu Jun 8 10:41:59 EST 1995


In article <3r2cqg$no0 at falcon.ccs.uwo.ca>,
 ovanham at julian.uwo.ca (o.   van-ham) wrote:
>
>I've been finding that when I run my sequencing gel for relatively long 
>runs, the temperature (and current) steadily drops.  I've heard that this 
>is due to a pH change in the buffer (TBE).  Is this true?  If so, how do I 
>remedy the problem.  The situation is complicated by the fact that the 
>buffer is hot (P32) from the samples.
>
try using a 'constant power' power supply. a proton gradient is formed
during electrophoresis and the resistance of the gel increases. at a
constant voltage, the current will drop and the temperature will fall.  if
one runs gels at constant power, the increase of gel resistance results in
a simultaneous voltage increase to maintain a constant wattage.  a side
benefit is that when the wattage is set correctly (depends on ytour rig
and the ambient temperature of the room), the gel stays at a constant
temperature.  also, since the voltage is slowly increasing, the gel starts
running faster and faster.  get a power supply that goes to 3000V with a
constant power setting (4000V is even better for really long runs), or
watch the current every 30 minutes or so and adjust the voltage upward
manually.

jeff

-- 
jeff lawrence
lawrence at bioscience.utah.edu



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