Water as Buffer? was "Oligo stability..."

Dr. Peter Gegenheimer PGegen at UKans.edu
Fri Aug 14 18:59:12 EST 1998


On Wed, 12 Aug 1998 17:40:17, hroychow at NMSU.EDU (Hiranya 
Roychowdhury) wrote:

> At 11:05 AM 8/12/98 +0100, Richard P. Grant wrote:
> 
> >Pure water is pH 7.0 by definition.   (Equal concentration of H+ and
> >OH-).  If your pH meter reads 6, then it is the pH meter that is failing,
> >not necessarily the water.  And I will add that most pH meters cannot give
> >a precise reading in such weakly buffered conditions, so do not feel that
> >you have an inferior product!

> >Cambridge Molecular          

Not a good advert for your Cambridge Molecular! The pH of water 
freshly obtained from a deionization system should be acidic, 
generally between pH 5.5 and 6.5. Water takes up CO2 from the air, 
which slowly converts to carbonic acid. This lowers the pH because 
water isn't buffered. To speak somewhat facetiously (?), if your 
purified water is not acidic, you don't have any CO2 in your air--is
anyone breathing? 

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