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Topic: Why pH goes down?  (Read 3775 times)

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Offline biostech

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Why pH goes down?
« on: May 20, 2010, 05:02:18 AM »
Hi. I have a typical biological solution of PBS1X + DMEM + HEPES buffer (buffer range 6.8-8.2).
After 1h adding glucose at different amounts, I obtain an acidification down to 5.9.

Why goes down?
Why goes down even with buffers?

Thanks in advance

Offline Dan

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Re: Why pH goes down?
« Reply #1 on: May 20, 2010, 05:26:38 AM »
PBS1X + DMEM + HEPES buffer (buffer range 6.8-8.2).

Sorry for the ignorance, but what are these things?
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Offline biostech

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Re: Why pH goes down?
« Reply #2 on: May 20, 2010, 05:46:57 AM »
PBS: Phosphate Buffer Saline (buffers around 7.4 pH)
DMEM : Dulbecco's Modified Eagle Medium it's nutrient solution with osmolarity suitable for cells
HEPES: it's a molecule that buffers around 7.48 pH
The entire solution is put at 7.5 pH. None of those acidify for sure.
Then glucose is added and pH drops

Offline Biopolmonkey

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Re: Why pH goes down?
« Reply #3 on: May 20, 2010, 07:06:08 AM »
Hmmm ... Honestly, I have no idea what is going on. Glucose itself is neutral, and should have no effect on the pH.

If presented with your observations I would probably do the following:
1 - Check the integrity of my chemicals.
2 - Add glucose individually to the PBS, DMEM and HEPES and see if it's maybe reacting (!?) with something in one of them.

Is there glucose in your DMEM?

Offline Doc Oc

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Re: Why pH goes down?
« Reply #4 on: May 20, 2010, 09:03:20 AM »
I just checked and DMEM appears to have amino acids in it.  Is it possible that the glucose is being oxidized to the acid?  Maillard-type reaction?

Offline Biopolmonkey

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Re: Why pH goes down?
« Reply #5 on: May 20, 2010, 09:11:16 AM »
You can get high glucose DMEM, so it is unlikely to break it down unless it has gone off or is contaminated.

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