Ethanol precipitation
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Ethanol precipitation is a method used to concentrate DNA, since DNA is insoluble in ethanol and precipitates. Isopropanol can also be used.
The initial precipitation is done with 100% ethanol (EtOH). This will precipitate DNA as well as the salts that form a ionic bonds with it. In a second step, the precipitated pellet is washed with 70%-80% EtOH, which will still precipitate the DNA but remove the salts.
Basic Protocol for Ethanol Precipitation
- Add 0.1 volume 3M sodium acetate (NaOAc), pH 5.2 to the DNA to be precipitated.
- Add 2.5 volumes 100% ethanol (EtOH) or 0.7 volumes of isopropanol and mix gently by inverting.
- Incubate 10min on ice. Smaller DNA molecules may require incubating at lower temperatures for as long as overnight for efficient precipitation. Carriers, such as tRNA or glycogen can also be used to maximize the precipitation efficiency.
- Centrifuge 20min at max speed on a benchtop microcentrifuge at 4°C and carefully aspirate the supernatant.
- Wash at least once with 70% EtOH, centrifuge again and aspirate supernatant.
- Air-dry 30min or using speed-vac and re-suspend in an appropriate volume of Tris-EDTA (TE)
See also
- DNA extraction
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