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Days old culture, removal of CO2, pH rise or drop? - (Apr/20/2012 )


I have a question regarding the pH of media.

How does the pH react when culture media is taken out of the incubator when it has been cultured at 37C with 5% CO2 for several days and starts to turn yellow/orange.

Normally, when fresh culture media is taken out, it increases its pH due to low CO2 concentration and the bicarbonate in the media, and returns to normal with 5% CO2. Now what happens if the media, based on phenol red, starts to become more acidic after several days of culture, and you take away the CO2? Will the pH go back up? Or does the buffer capacity decline and therefore, the pH drops even further?

Hope someone can give a simple answer.

Thank you.


The buffering effect of CO2 +H2O is not strongly limited by the pH, other than that the more acidic the medium, the less CO2 will dissolve to form the carbonic acid form. To cut a long story short, the pH should still increase.