A high-quality DNA sample is essential for a range of downstream applications such as PCR and sequence. DNA purification is a process that eliminates contaminants from a sample, including proteins or other cells' components. This produces an nucleic acid solution that is ready to use. There are a myriad of DNA purification methods each with its distinct advantages and disadvantages, based on the base material or the application.

The first step in DNA purification is to remove proteins from the sample by using the proteinase (protein enzyme) or mechanical disruption. After removing the cellular debris, DNA is precipitated using ethanol, resulting in an elongated white precipitate. The DNA that is precipitated is returned to the water or buffer that is sterile. The DNA concentration can be determined by spectrophotometry using the peak of nucleic acid absorbance at 260nm.

Another popular method for DNA purification is salting out, where a cellulose column is used to capture and bind DNA. The cellulose matrix is treated with detergents to eliminate contaminants, and a wash buffer is used to wash away the salts. DNA binds to matrix at low salt levels and contaminating proteins as well as DNA can be eliminated with higher salt solutions. The eluted DNA and RNA are then recovered through ethanol precipitation.

Anion exchange is also a popular method for purifying DNA. This method makes use of resin that attracts positively charged molecules of DNA, while an agent that neutralizes negatively charged molecules of DNA is used to cleanse the column. After the DNA has been removed from the anion exchange column, it can be filtered by centrifugation and then washed with ice cold 70% ethanol to precipitate the DNA.