RNA wash: 75% EtOH or 100% EtOH? - (Nov/20/2008 )
I'm using Trizol to extract RNA. For the final ethanol wash, can I use 100% EtOH before resuspension in water or buffer? I want to almost completely dry out my pellet before resuspension, but I always get a few microliters of liquid left with 75% EtOH. I'm hoping maybe 100% EtOH will dry out more.
The reason you use a 70-75% ethanol solution to do the final wash is to remove salt ... salt only dissolves in water and the 25-30% water component of the ethanol mix is enough to remove excess salt. Salt can inhibit downstream applications such as PCR etc.
If you have a few microliters left over and this is going to cause a hassle, use an pointed edge of kimwipe (lint free) tissue to absorb the water (do not touch the pellet of course). As it will be water remaining, maybe just add 2 µl less resuspension volume and verify final volume after the RNA has had time to dissolve.
Hope this helps,