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Medium PH - (Nov/22/2007 )

Dear Forum,

We have a problem with medium pH, as we know that every medium has its pH specification. We prepare the medium using rehydrated medium from common supplier, then we just doing like the instruction on its label (there is no instruction to adjust the pH, so in my opinion the pH after sterilization should comply with its specification without adjustment). But when we check the final pH after sterilization, it becomes out of specification. Is there something wrong?
Should we adjust the pH? How (we know that it is sterile medium)?
Can we still use the medium because its good in GPT although the pH is out of specification?

Thank you very much


The pH of a medium is usually checked prior to sterilization. The pH changes during autoclaving. But usually there is no drastic change in pH after autoclaving. A variation of 0.1-0.3 is observed sometimes.


You check it in the incubator and adjust the pH with NaOh or HCl.


Hot medium has a slightly lower pH... So u have to adjust the pH before autoclaving... U can do this with 1N HCL or 1N NaOH. Thou the manufacturers give a specific pH in the media container, the final pH of the media u prepare depends on the water u use... if the water is acidic or alkaline, the pH of the media will not be the one specified... But the specified pH is a must, as growth is dependent on pH also...


Thanks for your suggestions.
We have already adjust pH before sterilization as specified in the label, but the pH always decrease so it will be lower than specification. As information, we measure the pH after the medium get cooled as room temperature. Do you have any idea about this?


what kind of buffering system are you using?

Shouldn't the media's buffer system limit the pH change?


We didn't use any buffer, we just use purified water as specified in anhydrated medium preparation instruction. Is it necessary to add buffer?


what media are you making? what does the supplier say about the pH? what pH do you need? how far out of specification are you?