how to check if siRNA is intact - (Dec/08/2010 )

Hello all!

I have been doing some transfections with siRNA I purchase from qiagen in HeLa cells. My knockdowns were working well, I was observing %50 to %90 downregulation on WB.

Later I have ordered the very same siRNA, now I do the same procedure but I cannot get any downregulation. It , of course, could be a technical problem I am creating but I was wondering if I can check whether the siRNA is degraded or not.
Could you suggest something to check it?
Also I would appreciate any comments.

Thanks in advance!

can I see on the agarose or polyacrylamide gel maybe?