You have it right. The issue is that silica dissolves at pH >7.0 so you
need to get the pH down and a water wash removes the high salt and doesn't
use up a lot of the equilibration buffers. Since we generally give the
buffers away (in small quantities) or teach you how to make them rather
than sell them, we want to conserve as much of the supply as possible!
The other advantage of a water wash is that some researchers want to store
the cartridges before reuse. Thus a water wash puts you in the position
to either add ethanol for storage (without precipitating the salt) or
simply storing with water without running the risk of salt pptn from
The equilibration step then is the N2 as you describe (low salt pH 6.3)
which conditions the ion exchange surface to retain the nucleic acids of
As silica ages from this you will find the flow rate dropping, or the
capacity dropping so beware of getting too much of a good thing, and
certainly don't use the cartridges for different preps. They were made
disposable to prevent cross contamination, and not as some would want to
believe, to make more money.
All this is on our WWW URL under "protocols and applications">NucleobondAX
so if you want to add the bookmark you need not remember the details until
needed (I know the competition is always looking there for answers!).
In article <peter.85.30B1736A at chempath.uct.ac.za>,
peter at chempath.uct.ac.za wrote:
> Some time ago I came across a web site describing the reuse of Nucleobond AX
> DNA purification columns. Unfortunately I lost the details of the address.
> Could anyone here supply me with that address? Also, has anyone tried this
> protocol and what is the general consensus of its affectiveness? As I
> recall, the protocol involved washing the column with dH2O after the normal
> elution step and then either re-equilibrating with buffer N2 for immediate
> reuse or washing again with 50% EtOH and storing at 4C.
>> Peter Davies BSc (Med)(Hons)
>Peter at chempath.uct.ac.za
Hope this helps.
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