Ethanol precipitation is a method used to purify and/or concentrate RNA, DNA, and polysaccharides such as pectin and xyloglucan from aqueous solutions by adding salt and ethanol as an antisolvent.
In DNA extraction, after separating DNA from other cell constituents in water, DNA is precipitated out of solution by neutralizing it with positively charged ions. The addition of ethanol to the solution is necessary to reduce the polarity of the solvent and allow the positively charged ions to interact with the negatively charged phosphate groups of DNA.