Electrophoresis of dsDNA and ssDNA

[Paul J. Phelan]

I have a simple question that so far does not seem to have a simple answer.
I need to confirm that a 60-mer dsDNA oligo is double-stranded.
This is poly-dA/dT DNA.  Does anyone have a straightforward 1D 
electrophoresis protocol that will separate single-stranded and 
double-stranded forms of an oligonucleotide in the same range as a 
60-mer oligo?
I have already been surprised to learn that in 7 M urea PAGE, ssDNA 
will run SLOWER than dsDNA.  Does anyone have experience with this?

Thanks in advance,

Paul