For preserving DNA, you'll want to go with strong ethanol, minimally 75%.

Adding a little mild base (sodium bicarbonate-baking soda, calcium
carbonate-powdered limestone, etc.) would help counteract any acidity
in the preservative, but the exact results would depend on just what
has been added to it.

--
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"

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