desalting DNA

Wolfgang Schechinger Wolfgang.Schechinger at
Tue Jun 1 09:06:58 EST 1999

Hi Craig, 

What actually is your application?

I suppose that some salts are soluble in 70% EtOH to a certain 
extent, thus one should get rid of them with two additionaal 70% 
On friday I was talking to some guys from Perking Elmer 
concerning the salt content of samples for their "prism" capillary 
DNA sequencer since salt would as well as non deionized formamide 
lead to a decrease in electrochemically driven injection of DNA. They 
told me that two washes with 70% EtOH after a prec. with 2.5 vol 
EtOH would be sufficient. The temperature of the washes would be more 
critical since at low temp (-20°C, as often recommended) solubility 
would be lower for most salts. They recommended performing at least 
the washes (not the prec itself) at room temperature.

Anyway, you could try even a lower conc of EtOH for the washing. I 
don't think that DNA once precipitated would go into 
solution under these conditions. To be sure not to loose important 
samples, check out with some µg of plasmid and incubate with 
diluted EtOH. If you have access to fluorescently labelled DNA, you 
could start an even more sensitive assay and directly detect 
dissolved DNA in the supernatant. Or simply transform the S/N after 
evaporation into bacteria and see what will grow.


> From:          BGYCSW at (C.S. Wilding)
> Subject:       desalting DNA
> Organization:  University of Leeds
> Date:          Tue, 1 Jun 1999 10:54:51 +0100 (BST)
> To:            methods at

> Hi,
> I know there has been a bit about this already but...
> I don't think 2X 70% etoh washes are satisfactoraly washing my DNA
> extractions and am looking for alternatives. Are there any kits that
> allow either dialysis in a convenient format (easy to get the small
> vols back from whatever dialysis is performed in), or some kind of
> column. Cost is an issue due to the high number of samples. As for
> the washes, if you precipitate your DNA with 2 vols etoh you have
> 67% etoh. Why then would washing with 70% remove any salt that had
> precipitated. I would have thought that something less concentrated
> is necessary, although I can see that this is not possible unless
> you want to redissolve the DNA. Craig
usual disclaimers apply * This message is RNAse free - please don't touch!
Wolfgang Schechinger   
Pathobiochemistry Dept.      
University of Tuebingen, Germany
email: wgschech at * wwWait:
*unsolicited mail is *NOT* appreciated

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