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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: biostech on May 20, 2010, 05:02:18 AM

Title: Why pH goes down?
Post by: biostech 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

Title: Re: Why pH goes down?
Post by: Dan on May 20, 2010, 05:26:38 AM

Quote from: biostech on May 20, 2010, 05:02:18 AM

PBS1X + DMEM + HEPES buffer (buffer range 6.8-8.2).

Sorry for the ignorance, but what are these things?

Title: Re: Why pH goes down?
Post by: biostech 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

Title: Re: Why pH goes down?
Post by: Biopolmonkey 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?

Title: Re: Why pH goes down?
Post by: Doc Oc 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?

Title: Re: Why pH goes down?
Post by: Biopolmonkey 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.