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Namjin Chung nc1 at acpub.duke.edu
Tue Jan 28 10:53:43 EST 1997

Leibowitz wrote:

You can buffer YPD at almost any pH using various phosphate or citrate buffers. 
However, if you plan to pour plates, add the buffer after autoclaving, since at
extremely acid pH, the agar will be damaged under autoclave conditions and the
plates will never solidify (and they are really messy to discard!).
You will need to test how much buffer to add; I have never done the whole range
of pH values.

Mike Leibowitz
UMDNJ-RW Johnson Medical School

Dear Dr. Leibowitz and others who may be interested in pH-adjusted media,

Overall I am in accord with Dr. Leibowitz, but I have found some practical
problems while I tried to make YPD or SC with acid pH.  I hope there will
have been some discussions about this so that we could get a recipe for
pH-adjusted media:

First, since medium ingredients themselves can affect pH, I could not get
the pH I want after adding correct ratio of buffer solutions.  I tried to
make YPD or SC with pH 2.0 by adding citrate-phosphate buffer, but I found
that actually I got pH 3.5 after measuring pH.  I hope there could be
standard recipe for how much buffers being added to media to get different

Second, the difference between supposed-to-be pH and actual pH make it
difficult to make plates.  As mentioned above by Dr. Leibowitz, pH for
plates should be measured after autoclave.  However, if you don't get the
pH you want after adding, for example, x mL of Buffer A and y mL of Buffer
B according to buffer recipes, you probably need to use pH meter and
re-autoclave again.  I never tried this before, but is it alright to
autoclave twice.

Third, after I votexed vigorously YPD broth and adding buffer to get
acidic pH, I got some precipitates while SC media was clear after being
adjusted to acid pH.  Does this mean that I should add buffer after
autoclaving to make the YPD?

Thank you for the attention.

Namjin Chung, who knows little and asks a lot!
Program in Molecular Cancer Biology
Duke University Medical Center
Durham, North Carolina

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