[biostech]

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

[Dan]

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

Sorry for the ignorance, but what are these things?

[biostech]

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

[Biopolmonkey]

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?

[Doc Oc]

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?

[Biopolmonkey]

You can get high glucose DMEM, so it is unlikely to break it down unless it has gone off or is contaminated.