I want to prepare a TRIzol-like buffer for RNA extraction. In the buffer recipe it's written that I have to prepare a 0.75 M sodium citrate stock solution with pH 7.0.
Initially, I only wanted to double check which acid to use for pH adjustment but after reading several articles about sodium citrate and citrate buffers online I got confused about how to prepare this stock solution.
I thought I can easily do it like this:
For 150 mL stock solution, dissolve 33.09 g of tri-sodium citrate dihydrate (M = 294.1 g/mol) and adjust the pH.
But now I am not sure anymore if it's that easy...
My first question:
Which acid should I use for pH adjustment? Citirc acid? But then I would also alter my citrate molarity I guess.
HCl? But then I will have chlorid ions in my solution?
Second question - more general:
How do you prepare a sodium citrate solution with pH 7.0?
Hi there,
You may in theory make a solution of 0.75M tri sodium citrate and then adjut pH with 0.75M citric acid if the pH is actually higher than 7 (which I'm not sure of...). If you do it that way, total citrate will remain 0.75M. Alternatively, I would go for preparing adequat citric acid, mono sodium or di sodium citrate solutions, adjust pH to 7 with NaOH and then adjust final volume so that final citrate concentration is 0.75M.
Hi Dominique,
thanks for the answer! I have a few more questions.
Which molarity of citric acid do you suggest when I want to use citric acid for adjusting the pH? 0.75 M, too?
And what do you mean by adequat citric acid solution? 0.75 M citric acid solution?
We only have tri-soidum citrate (and citric acid) in the lab. Will there be a big difference to mono- or di-sodium citrate? (Actually, the recipe I got only says 0.75 M sodium citrate but nothing about mono, di or tri...)
Hi again,
To keep citrate concentration at 0.75M, you have to use citric acid at 0.75M to adjust pH.
By adequat solution I mean solution containing enough product to get 0.75M citrate at the end (ie. after adjusting the final volume).
If you start from citric acid you will use more NaOH to adjust pH at 7 as you will have to neutralize the three acidic function of citric acid (whereas mono and di sodium have already one and two acidic functions already neutralized, respectively).
https://ar.wikipedia.org/wiki/%D8%B3%D8%AA%D8%B1%D8%A7%D8%AA_%D8%A7%D9%84%D8%B5%D9%88%D8%AF%D9%8A%D9%88%D9%85
Lena, try this link, it may be helpful:
https://www.aatbio.com/resources/buffer-preparations-and-recipes/citrate-buffer-ph-6
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