Saturated O2 concentration in Tris buffer?

Justin Powell jacp1 at
Fri Oct 24 10:18:45 EST 1997

"Jonathan B. Marder" <marder at> writes:

>Justin Powell wrote in message
>+AD4-I need to know the concentration of oxygen in air saturated 50mM
>+AD4-pH7.6 buffer at 25C in order to interpret some oxygen electrode data I
>+AD4-have.  ...

>You can easily try by comparing the reading you get with air saturated
>distilled water vs. air-saturated buffer. I don't know for sure, but I'd
>be very surprised if the buffer has any significant effect at all i.e.
>the O2 conc. at this temperature would be around 0.26 mM.

I'm not sure that comparing the reading with air saturated water works. 
O2 electrodes measure the chemical activity of O2 rather than the
concentration and so for example the O2 electrode with air saturated 1M
KCl will give a value 99% of that of air saturared water even though the
actual concentration is only 73%.  Comparing with distilled water would
only be valid if the activity co-efficient is close to one for 50mM Tris
and I am not enough of a chemist to know the answer to that.

Regarding buffer effects generally I had looked up the effects of salts on
solubility of O2 and while some do not affect the value significantly
others can halve it at concentrations as loow as 125mM - sadly the data
book did not include values for Tris. 

Justin Powell
Dept. Genetics

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