Buffer preparation - Problem with EDTA (Oct/04/2007 )

h! All
i m preparing buffers for DNA isolation, one is STE (NaCl, Tris,EDTA) and another is TE, by dissolving Tris and EDTA separately, i used disodium salt of EDTA and it gives pH about 4.75 which is very less and not useable for me, i have to set the final pH of buffer at 8, Tris-Cl part is ok at 8
so sholud i use EDTA without disodium salt of here is any other way out, and i think NaOH can not be used in this, which i never heard or learnt from literature,
so please tell me what can be done here.
tris is 10mM and EDTA 1mM
thanks.....

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EDTA is alaways used at pH 8.0 by using NaOH. Also, pH 8.0 helps the solubility of the compound.

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Why NaOH cannot be used???? You need to make stock solution for the required components (Tris, EDTA, NaCl), and adjust pH when necessary (for Tris and EDTA), then mix them together with the right amount to make the final solution. As you said, the EDTA you used is sodium salt. So adding NaOH in would help change the pH, but it would not cause any additional ion type, so what is the problem?

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pH 4.75 is quite normal for EDTA-2Na. What is the concentration of your stock? With EDTA-2Na in high concentrations you usually have to add lots of NaOH to get it in solution (best arround pH8.0)

As you have NaCl anyhow in your solution, why should NaOH harm? It the standard way to adjust the pH of EDTA solutions....

Don´t use EDTA free acid.. it is less soluble and even more acidic.

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