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Sodium Acetate Buffer - (Mar/07/2013 )

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Hi all,

I need to prepare sodium acetate buffer 3M at pH=5, I have sodium acetate tridydrate (PM 136,08 g), can I prepare it from this one?
I have tried to prepare 50 ml, but find quite difficult to dissolve it and also difficult to adjust the pH with HCl 37%, could someone help me please?

Thank you very much

-vanu-

Usually this is prepared by dissolving the acetate (it will take a while and you need to leave quite a bit of volume for pHing) and then adjusting the pH with glacial acetic acid. This will result in the buffer being 3 M with respect to sodium and 5 M with respect to acetate.

-bob1-

═ don┤t really understand what you mean. I have weighted 20.42 g of Sodium acetate trihydrate and have tried to dissolve it in 50 ml, is that right?

-vanu-

For a total volume of 50 ml that is correct, but you need to leave some space (volume, see below) for adjusting the pH. Sodium acetate when dissolved will not be pH 5,0.

This is the recipe I have for 1 L of 3M NaOAc using the trihydrate form, change the pH to suit yourself:

3 M NaOAc – 1 liter
Dissolve 408.24 g sodium acetate – 3H2O (NaOAc – 3H2O, MW = 136.08) in 800 ml H2O.
Adjust to pH 5.2 with glacial acetic acid or to pH 7.0 with diluted acetic acid.
Adjust volume to 1 liter with H2O.
Sterilize by autoclaving and store at room temperature.

-bob1-

But I see I should use glacial acetic acid in order to adjust the pH instead of HCl, shouldn┤t I?

-vanu-

vanu on Thu Mar 7 21:42:52 2013 said:


But I see I should use glacial acetic acid in order to adjust the pH instead of HCl, shouldn´t I?

yes.

-bob1-

OK, thank you very much!
Do you warm the solution in order to better dissolve it?

-vanu-

You can, but it should be OK without heating. It will be quite a thick (viscous) solution, a bit like glycerol.

-bob1-

ok I will try it again, thank you very much for your help Bob!

-vanu-

bob1's recipe is the standard molecular biology formulation for sodium acetate (used for such things as precipitation of nucleic acids, where sodium concentration is more important).

if you want to prepare a sodium acetate buffer (where acetate is the more important component) then you can prepare 3M sodium acetate and 3M acetic acid (dilute from glacial (17.416M), you can use this calculator from sigma-aldrich) and mix them until you reach the desired pH. acetate concentration will be constant, regardless of volume, sodium will be variable.

you can find buffer tables for acetate buffer (among others) in the attachments in this previous post.

-mdfenko-
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