SDS PAGE Voltage Problems

Hello,

I am a Master's student in Chemistry and have been having some trouble running 20 cm x 20 cm SDS PAGE gels (1D).  The problem is that the voltage of the gel while it is running remains extremely low throughout the run.  Currently my power supply is set to have current as the limit however while I run my samples, the voltage never exceeds the mA (if I have it set at 20 mA the voltage will stay consistently at 19-21).  Usually the voltage would start low and increase slowly throughout the run.

For example, I ran a 20 x 20 gel and it took 8 hours for the tracking dye to reach about 1/2 way down the gel.  Throughout the entire time the voltage remained low (about 30 when the limit was set to 240) I checked my gel 2.5 hours later and the voltage was up to 240 and all of the proteins had run completely off the gel.

I had samples that contained very high salt concentrations so I diluted the samples 1:10 with water but the problem persisted.  This is not a problem I have on the smaller (10 cm x 10 cm) gels.

Unfortunately no one in my research group nor my advisor has ever encountered this problem so I would very much appreciate any input.

Thanks!
Kathleen

 HI

High salt content is the main culprit for the same. You can set your SDS PAGE for a constant voltage rather than using constant current.

ALternatively, precipitate your protein for removing salt by TCA/Acetone, resolubilize the salt depleted protein and then load.