sds page gel shrinks when casting

[bwalker]

Hi, I'm trying to cast my own gels for sds-page, but my gel shrinks when I cast it. For example, I follow all casting instructions for a 7%T gel, pour the solution all the way to the top of the gel cassette, then insert the comb. But 1 hour later, the gel has shrunk to the point where it is below the comb.

Can anyone think of why I would be having this problem? It makes sense that the gel should shrink a little while polymerizing, but not to the point that I'm seeing it. Maybe my acrylamide is old?

Thanks,
Brandon

[butters]

Can you list out your formula for us to have a look? and is your APS freshly prepare?