This is the smear in 10% TBE-Urea gel. The lane in the picture was my control with only the oligo (57 nt). Last time I ran the same oligo with 15% TBE-Urea gel and got a clear band as it should be. However this time it is only the weird smear here.

Some details:

1. I've pre-run the gel at 180 V for 45 min.

2. The loading buffer was Novel TBE-Urea buffer (2x). I also tested with formamide and I got the same result, so the buffer should be no problem.

3. I heat the sample at 70 degree for 3 min before I load them.

4. I also cleaned the wells with pipette before loadding the samples.

Today I just did the electrophroesis with 15% TBE-Urea gel again, but I got the same kind of smear this time.