Some problems of DNA recovery from native PAGE gel

[wusilinqi]

My protocol of the PAGE gel running and DNA recovery is as follows,
1. 20% native PAGE gel (The DNA i want to purify is around 20bp dsDNA + 10 bp ssDNA )
2. running at 250 v for 30mins,
3. stain and cut the desired band;
4. cursh the gel by yellow tips into small gains;
5. add 2volume TE buffer (100ug gel ~ 200ul TE buffer)., rotating the mixture for overnight at room temperature (~24C);
6. centrifuge the mixture at 12000g for 15 min;
7. take out the supernatant, and the DNA should be in it.

The problem is that when I use nanodrop to measure the concentraion and check the purification, i found that only 10% DNA is recovered, and the product is not pure.
Please help me to find the mistakes. Thanks.

[domwood]

Well I'm no expert on this, but I would have thought the two key steps are the physical ones, the gel and the centrifugation. Have you tried running the gel at a lower voltage over a longer period, and also centrifuging for longer.

Also what is the source of the DNA, can you be sure of the extraction method's efficiency?