Self-made closed bottle pressure calibration

Off-topic conversations and chit-chat.

4 posts Page 1 of 1
Dear all

This is not chromatography related, but I know there is other lab hand-work experience around here :)
Here is the challenge: We have pressure sensors for bottles we use in CO2 evolution tests used for biodegradability studies. The volume of every bottle is determined individually and a known amount of water is added so that the pressure is proportional to the amount of gas evolved. These sensors are calibrated using VERY expensive tablets that look a bit similar to effervescent tablets, only smaller. We have tried to use Magnesium tablets from the drugstore (larger, but work), but these show relatively high variation in the final pressure, so they cannot be used for calibration.
I thought about adding a known amount of analytical grade hydrogen carbonate and excess acid to allow quantitative formation of CO2. Problem: The gas evolution starts before I can close the bottle tightly. I need something which delays the gas formation. Any ideas are greatly appreciated.

Thanks
Jörg
Can you put the hydrogen-carbonate in a little aluminium weigh-boat or a small plastic tube fixed to the underside of the lid, so you can screw the lid on and then tip the bottle?
what about hard-gelatine capsules to wheigh in the carbonate?
these should dissolve slowly and release the carbonate to the acid.

Another thing I wonder about the set-up:
Did you take into account the amount of gas which will dissolve in the water?
Hollow wrote:
what about hard-gelatine capsules to wheigh in the carbonate?
these should dissolve slowly and release the carbonate to the acid.

Another thing I wonder about the set-up:
Did you take into account the amount of gas which will dissolve in the water?


Gelatine capsules are a great idea, they cost almost nothing and should be easy enough to fill with accurate amounts of cabonate.
The amount of gas in the water should be negligible at pH <= 2, but of course we will have to check the literature for equations.

Thanks a lot
Jörg
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