I tried to prepare seawater agar. It is written in the receipt that adjust pH to 7.8, but I measure pH 6.5. How can I adjust pH in seawater agar?
You cannot adjust the pH once you have made the agar.
Adjust your pH first, then add the agar, autoclave and then pour plates, slants whatever you need.
Just before you pour the agar out take about 100uL and check the pH using pH paper to confirm you have the pH you need. Do NOT dip a pH meter probe into the molten agar, it will spoil it.
You can not adjust the pH, if the medium already contain agar in it. Get seawater broth medium and adjust the pH before adding agar.
If getting sea water broth medium delays your experiment. Take aged sea water (sea water kept under dark for (2 to 4 weeks) and add nutrient broth in to the sea water and adjust the pH to 7.8 then add agar. This medium can be used to isolate marine microbes. If you are working with coastal microbes, then use 50% aged seawater (50% Distilled water and 50% sea water).
Dear Dr. Toorkey and Dr. Thavasi,
many thanks for your conributions. I asked the question in wrong way sorry. I would like to learn also, which chemical should I use to adjust pH in broth medium. I mean, is it correct to use NaOH, HCl, or tris? Which one is more appropriate, I think tris is more convenient than the others. In addition the which molarity should be used for this chemicals.
Hi, Ilknur, add few drop of NaOH (under the pH-meter). The amount of NaOH will dependent from buffer capacity of the medium.
Try to start with 0.5 M naOH and add not more thna 1 µl/ml to avoid too high pH.
I agree with Dr. Pasternak's suggestion.
An easy way to do it is to take about 10 - 25 cc from your major volume in a small beaker and slowly add 1.0 or 0.5 NaOH using a micropette.
Note how much you had to add to adjust the pH of that volume (10 - 25 ml) and then add appropriate amount to the larger volume.
Dr. Pasternak and Dr. Toorkey many thanks for your suggestions. They will really help me. In addition can I decrease the pH with HCl vice versa? Or I can not use both NaOH and HCl in the same broth. If I need to decrease pH again in the same broth, will I create salt with HCl and NaOH?
Provided the amount of HCl and/or NaOH you add are small there will not be cause for concern. Remember it is always easier to adjust the pH of a buffered medium (either organic or inorganic) and add small volumes at a time.
Good luck. God bless.
Dr. Toorkey thank you for your help. I woul like to ask some questions more to be sure. In media receipt, it s written to solve beef extract and pepton in tap water by heating. Adjust pH 7.8 ( I measure pH around 6.5 in this time). Then it says boil for 10 min. Readjust pH to 7.3. Add agar and autoclave.
But I encountered two problem. one of them is that; when I cooled the broth media, pH was getting higher (from 7.3 to 8.3). Is it correct to adjust pH while heating the broth media or I shoul do it when the media is cooling down? The other problem is, the media became solid a soon as adding agar. Could you please show the way which I should follow?,
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