Ethanol is a widely used to purify and concentrate the DNA from the aqueous solution (in some case isopropanal).Basic principle is that when salt and ethanol are added to the solution, it forces the nucleic acid to precipitate out of solution. Salt (NaCl) Na+ interacts with the negative charge of DNA (Phosphorus) and neutralizes the negative charge nucleic acid and makes it less soluble. Ethanol has a much lower dielectric constant when compared to water, making it easier for Na+ to interact with the negative charge of phosphorus group of DNA and make the nucleic acid less hydrophilic, causing it to drop out of solution. The precipitated DNA can purify by centrifugation. The DNA pellet is washed in ice cold 70% ethanol to remove excess salt and pelleted is then allowed to dry and then dissolve in appropriate buffer or can stored in -80 for long term..
