# Approximating SDS-PAGE running times - (Oct/23/2008 )

Hello all - first timer here...

I've been running a lot of gels (8% mainly) the last few months and gotten into a good groove. However, there are times when I'd like to have more control as far knowing what volts will result in a running time for a particular gel (8%, 12%, etc.). Is there a formula where I can plug in my variables (volts, length, % gel) and get out of it an approximate time to completion?

If disregarding the stacking layer makes things simpler, let's do that. I've always assumed a linear relationship. That is, 50V will run distance X in time Y while 100V will run distance 2X in time Y. Likewise, an 8% gel is twice as fast as a 16% gel. Am I entirely off with my assumptions?

Thanks for looking and thanks for you help in advance!

Are these bought or self-poured gels? If bought, phone the supplier.

I think I'd have a play some quite (?) Friday afternoon or weekend and run a few standards at different mVs. Then do the mathematical modelling. Then publish. Then collect more funding. Then appoint students...

you will not find a linear relationship with varying voltage, maybe with varying current, possibly with varying power.

but

a number of factors, such as heating, cooling, buffer formulation, pH, etc, will affect run times (and resolution).

as paraboxa said, you can spend some "quiet" time and run gels under varying conditions to try to develop a formula to approximate running time.

or

just continue as you are.

Thank you both for your replies. I may have to spend some time running gels and carefully observing times and dye line behavior as suggested. My initial observations suggested that there was a predictable method to the madness. Oh, and to answer some questions:

> These are self-poured gels

> We run the gels at about standard room temperature

> We run the gels at constant voltage with varying amperage

Well, thanks again for your replies. When I get some good results I'll post back.

what i meant here was varying

__constant__voltage, varying

__constant__current and varying

__constant__power in your attempt to show a linear relationship.

pouring your own may allow for more gel-to-gel variation in running characteristics.