Ethanol precipitation

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 ethanol as an antisolvent.

DNA is polar due to its highly charged phosphate backbone. Its polarity makes it water-soluble (water is polar) according to the principle "like dissolves like".

Because of the high polarity of water, illustrated by its high dielectric constant of 80.1 (at 20 °C), electrostatic forces between charged particles are considerably lower in aqueous solution than they are in a vacuum or in air.

This relation is reflected in Coulomb's law, which can be used to calculate the force acting on two charges ${\displaystyle q_{1}}$ and ${\displaystyle q_{2}}$ separated by a distance ${\displaystyle r}$ by using the dielectric constant ${\displaystyle \varepsilon _{r}}$ (also called relative static permittivity) of the medium in the denominator of the equation (${\displaystyle \varepsilon _{0}}$ is an electric constant):

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