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agar polymerization


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#1 josephine

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Posted 24 June 2009 - 04:43 AM

Hello everybody!

I was wondering what could stop agar from polymerizing?
I poured plates (5g agar, 0,9 g NaCL in 100ml H20) and left them to polymerize but in 24 hours they are still half liquid! What did I do wrong?

#2 gebirgsziege

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Posted 24 June 2009 - 04:48 AM

(i) you forgot the agar (happens more ofthen than you might think).

(ii) if you are only using 5g per 1000mL you will only get a slurry. Usually 15 - 20 g per L are added (or are you really using 50 g/L?????).

(iii) your autoclave is not working and the agar did not dissolve.

(iv) the pH of your solution is to low. Agar does not polymerise at a pH smaller 4.5 (or was it 4?)

Edited by gebirgsziege, 24 June 2009 - 04:49 AM.

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#3 GeorgeWolff

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Posted 24 June 2009 - 12:56 PM

Agar is composed of polysaccharides that do not polymerize - they gel. The pH where is hydrolyzes and will not set is < 3.

Edited by GeorgeWolff, 24 June 2009 - 12:57 PM.


#4 gebirgsziege

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Posted 24 June 2009 - 09:56 PM

Agar is composed of polysaccharides that do not polymerize - they gel. The pH where is hydrolyzes and will not set is < 3.


You are right....sorry for sloppy language.

Thanks for refreshing the pH! Nevertheless when making media with a pH lower than 4.5 I would suggest to add some more agar (especially if you want to plate sth on it).

Edited by gebirgsziege, 24 June 2009 - 09:56 PM.

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#5 josephine

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Posted 24 June 2009 - 10:56 PM

yes, I really use this much, the plates are not for culturing anything but to glue tissue to while making slices.




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