Oligo stability in water at -20 C

Bryan L. Ford fordb at bcc.orst.edu
Thu Aug 13 02:58:29 EST 1998


Peter wrote:
> 
> In article <19980812151539.19492.rocketmail at send102.yahoomail.com>,
> rjdudley at yahoo.com wrote:
> 
> > The definition is true; however, Milli-Q is not "pure by definition"
> > water.  There are dissolved gasses (e.g., CO2, N2, O2).  CO2 is of
> > special importance, since it does play a role in buffering water (and
> > your blood) with the carbonate-bicarbonate buffering system.  The mere
> > act of retrieving water from the Milli-Q tap intorduces CO2.
> > Adidtionally, I don't think that Milli-Q (or other deionization
> > systems) scrub protons; they are more geared for nitrates, sulfates,
> > etc.
 
> Not true.
> Most Milli-Q systems have a .22um filter that is connected at point of
> dispencing, therefore, disolved gasses are virtually non-exsistant. 

So, Peter are you suggesting that the 0.2 micron post filter prevents
gases (with molecular diameters of a few angstroms or about 1000th of
the 0.2 micron pore size) from dissolving from the air back into the
outlet line?

Even if this assertion were correct, I think most lab personnel will run
the milli-Q at least a couple of seconds before drawing off the working
water. Or were you suggesting that the 0.2 is blocking protons-- with
effectove diameters as H30+ etc of again a few angstroms? In either case
it looks like Richard Dudley is at least not in error.

> Also
> if your conductivity meter is working correctly and it reads >18MOhms then
> it is safe to say you have no ions.

I assume you mean "no ions other than H+ and OH-".

> Because if you did have ions then you
> would see a conductance of less than ~17 MOhms. 

Terminology point: Ohms measure resistance not conductance. The Siemens
(or "Siemen" as commonly construed) is the unit of conductance and is
the
reciprocal of the Ohm.

> Also most Milli-Q systems have a cartirage that is called a "polishing
> cartirage".  It is made up of activated carbon which will bind to
> uncharged molecules.  It works by a priciple called "adsorption".

A fact left out here is that the adsorption works well, that is it is
very
efficient, because of the enormous surface area of the activated carbon. 

> With
> regard to carbon, all polar or species with lone pair electrons will
> bind. 

Should that read "all non-polar species"?

> The charged species that you mentioned will be removed by the initial
> cartridges which are made with Strong cation and Anion resin.

Carbonic acid (carbon dioxide is the anhydride of this acid) must be
present in most unprocessed feedwaters such as tapwater. In our milli-Q
apparatus the feedwater is steam distilled water and thus is quite low
in dissolved gases at the outset.

If one uses tapwater as a feed where in the Milli-Q system is carbon
dioxide/carbonate removed? Does anyone here know if CO2 itself adsorbs
strongly
to activated carbon?



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