July 18, 2019, 03:58:38 PM
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Topic: pH shift in a Buffer Confusion  (Read 371 times)

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Offline dbranch

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pH shift in a Buffer Confusion
« 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

Offline Babcock_Hall

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Re: pH shift in a Buffer Confusion
« Reply #1 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.

Offline Mitch

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Re: pH shift in a Buffer Confusion
« Reply #2 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?
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Offline jeffmoonchop

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Re: pH shift in a Buffer Confusion
« Reply #3 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?

Offline Babcock_Hall

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Re: pH shift in a Buffer Confusion
« Reply #4 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.

Offline Borek

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Re: pH shift in a Buffer Confusion
« Reply #5 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).
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