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

Hello,

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.