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Specialty Chemistry Forums => Biochemistry and Chemical Biology Forum => Topic started by: dbranch on May 17, 2019, 10:28:32 PM

Title: pH shift in a Buffer Confusion
Post by: dbranch on May 17, 2019, 10:28:32 PM
I resently made a Tris-EDTA buffer that is displaying an increase in pH as heat is applied. 5°C-->7.8, 25°C-->8.0, 37°C-->8.3. WWWHHHYYYY? To the best of my understanding, increased heat should increase ionization resulting inan increase in[H+] and a decrease in pH.

Help please, TIO
Title: Re: pH shift in a Buffer Confusion
Post by: Babcock_Hall on May 31, 2019, 02:59:42 PM
By itself TrisH+ increases in pKa as the temperature decreases, and ΔpKa/ΔT is about -0.03 pH units per degree Celsius.  I would consider the possibility of an error in standardizing the pH meter, but I am just guessing.
Title: Re: pH shift in a Buffer Confusion
Post by: Mitch on June 03, 2019, 03:11:59 PM
Right, this might be a pH meter issue. Do you observe the same issue with just water?
Title: Re: pH shift in a Buffer Confusion
Post by: jeffmoonchop on June 03, 2019, 03:48:15 PM
I heard tris is dodgy with regular pH meters and should use Calomel ones. Anyone know anything about that?
Title: Re: pH shift in a Buffer Confusion
Post by: Babcock_Hall on June 05, 2019, 09:40:45 AM
Buffers:  The Basics (RJ Beyond) mentions that not all electrodes are compatible with Tris, but it does not supply more information than that.
Title: Re: pH shift in a Buffer Confusion
Post by: Borek on June 06, 2019, 02:56:27 AM
Question is whether it is a matter of electrode glass (kind of a sodium error) or a reference (which is in general hidden behind junction or two).