0.2M EDTA 2Na pH 8.0 - (Apr/26/2007 )

Hello,

I know this is a very simple work to do, yet I`m stucked here with my EDTA solution (I`m preparing TNES urea buffer)
I was trying to make a 0.5M EDTA 2Na pH 7.5.
I added NaOH pellet and also 1N NaOH gradually while stirring the solution, but it didn`t dissolved at all.

So now I reduced the concentration into 0.2M
It looks better than the 0.5M one but it still doesn`t dissolve completely

Do I miss something in making this solution??
Or should I reduce again the concentration?

Really need your help
Thanks

Audrey

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Have to be pH 8, I suppose. Add more NaOH

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EDTA only dissolves at pH 8, maximum concentration 0.5M.

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hello, thanks a lot for your suggestions.

yes, I already added some more NaOH to reach pH 8.0
I even reduced the concentration into 0.1 M (I made a new one)
Yet I still found some white "things" floating on the solution.

Does it take very long time to make it completely dissolved?
I`ve been stirring it for more than 2 hours

Thank you
Audrey

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What is about purity grade of your EDTA powder and try to warm your solution on water bath till 60-80 C during mixing. Did you estimate quantity of EDTA correctly? About EDTA solution here is a product from FLuka that give 0,5M ( 03690) other salts like disodium tetrasodium and other give only 0.1-0,3M max. But 0.1M is standart solubility. but depends on pH.

Try this recipe: 0.5M, 1L: 148 g EDTA + ~30-40 g NaOH to adjust pH (or 186 g EDTA-Na.2H2O + ~20 g NaOH) Note: pH adjusted by NaOH is essential for solubility. Autoclavable.

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Try this recipe: 0.5M, 1L: 148 g EDTA + ~30-40 g NaOH to adjust pH (or 186 g EDTA-Na.2H2O + ~20 g NaOH) Note: pH adjusted by NaOH is essential for solubility. Autoclavable.
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hello circleone

I have tried these :

0.5 M ----> 18.61 g EDTA-2Na + 100 ml H20 -----> adjusted to pH 7.5 using NaOH -----> it didn`t dissolve (I could see the powder layer on the bottom of my flask)
0.2 M ----> 7.44 g EDTA-2Na + 100 ml H20 ----> adjusted to pH 8.0 using NaOH ----> it didn`t dissolve (the solution looked clearer but it still has powder floating everywhere)
0.1 M ----> 3.72 g EDTA-2Na + 100 ml H20 ---> adjusted to pH 8.0 using NaOH ----> i almost thought it dissolved, but it didn`t

20 g of NaOH?? what if it`s too much? I only added 3 NaOH pellets and it`s already reaching pH 7

I`m preparing TNES urea buffer and I need EDTA-2Na pH 7.5-8 for it (http://genome-lab.ucdavis.edu/Protocols/TNES-Urea.htm)



Audrey

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20 g of NaOH?? what if it`s too much? I only added 3 NaOH pellets and it`s already reaching pH 7





Audrey
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But only till 7 not 8 and this value may fall down a time. I think it is due to high buffer capacity of acetate residue

About 20g NaOH I found it here http://www.stanford.edu/group/gozani/Buffe...Preparation.pdf

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Hi, The 20g is for 1L, your few pellets were only in 100ml! If you look up maniatis you will see that ~20g is recommended for 1L, adjust this according to the amout of soln that you are making, after adding the pellets give it plenty of time to go into soln.

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500 mM EDTA, pH 8.0

186.1 g of Na2EDTA (FW 372.2)
20.28 g of NaOH (FW 40)
QS to 1000 mL dH2O

= 500 mM EDTA and 507 mM NaOH.
The amount of NaOH is based upon pKa calculations.
1-10 mM EDTA is soluble over a relatively wide pH range (pH 6 and up).

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EDTA's solubility is so limited below pH8 that you will have to go through a series of cycles of adding the NaOH, letting it dissolve, then adding some more, letting it dissolve etc. Check the pH all the way through and you'll see it cycling up and down, but always edging towards pH8.
Don't panic! Just keep on going and you'll get there.

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