The carboxyl groups of EDTA are not dissociated at low pH. Undissociated carboxyls (COOH) have no charge because the hydrogen is covalently bound and therefore acid EDTA is almost insoluble in water. You may use Na-EDTA, which is soluble salt. Or you make it by adding NaOH to EDTA - when the pH rises more carboxyls become dissociated (COO-) releasing protons (H+) to the solution (which is the principle of its pH buffering ability). Dissociated EDTA is ionic and thus water soluble. Note that there are four  carboxyls in EDTA molecule, "each" dissociates in different pH - pKa values are 2.0, 2.7, 6.2 and 10.3 (pKa means pH at which half of the carboxyls are dissociated).

But I see that this problem has been discussed earlier.

https://www.researchgate.net/post/I_have_been_preparing_05M_EDTA_ph_8_since_yesterday_and_it_is_not_dissolving_I_need_help_coz_I_seriously_need_to_prepare_TAE_buffer

The carboxyl groups of EDTA are not dissociated at low pH. Undissociated carboxyls (COOH) have no charge because the hydrogen is covalently bound and therefore acid EDTA is almost insoluble in water. You may use Na-EDTA, which is soluble salt. Or you make it by adding NaOH to EDTA - when the pH rises more carboxyls become dissociated (COO-) releasing protons (H+) to the solution (which is the principle of its pH buffering ability). Dissociated EDTA is ionic and thus water soluble. Note that there are four  carboxyls in EDTA molecule, "each" dissociates in different pH - pKa values are 2.0, 2.7, 6.2 and 10.3 (pKa means pH at which half of the carboxyls are dissociated).

But I see that this problem has been discussed earlier.

https://www.researchgate.net/post/I_have_been_preparing_05M_EDTA_ph_8_since_yesterday_and_it_is_not_dissolving_I_need_help_coz_I_seriously_need_to_prepare_TAE_buffer

Hi! The answers given here are comprehensive and sufficient.

But we can simplify otherwise: The EDTA acid is a tetraacid (H4Y) with a poor solubility (the most soluble form being H2Y2-, 2 Na+) and with increasing the pH (e.g. by adding NaOH), the  tetraacid dissociates (deprotonates) successively and gives H3Y-, then H2Y2-, then HY3- then Y4- (the tetrabase), and these species predominate (prevale) at pH values corresponding to the respective pKa values as follows:

H4Y predominates at: pH

I think the answers given are sufficient

I agree with med-amar(Amar) Mecherri.

usually sodium EDTA salts will be soluble in water

Is EDTA/HCl salt commercially available?

Jigui, your question makes little sense. HCl is a gas when not dissolved in water, and EDTA is an organic acid.

Both EDTA and sodium salts of EDTA are commercially available, however.

I think that the answer you're looking for it was given but probably there isn't a real explanation of what happens once you pour your EDTA in water.

I'll try to keep it simple:

1. the H4Y form It's NOT a salt so there can't be a Ksp, hence it isn't related to that

2. If you have 4 acidic constant (K1; K2; K3; K4) of which the first one is quite high once you put it in water, unless you do use a buffer, you're likely to be in this stage :

H3Y- (predominat); H2O and H+ at pH close to 2

3. if you look at the structure of EDTA all the carboxilc groups are protic and polar in the meantime , but there are still 2 effects, called steric and hydration, to be taken into account.

4. As the molecule is bigger than an inorganic salt such NaCl it's harder for the water to form an hydration sphere around H3Y- , hence water is not able to dissolve it. But when you can get a higher charge, by adding a Base such as NaOH and bringing the pH around 8, you specimen are mostly H2Y- and HY3- so that each negative charge can attract more water molecules and eventually dissolve the EDTA (H2Y2- form) completely.

Properly dissolving in water at pH 8.0 or above

Hi,

does anybody knows how good dissolved EDTA will bind to silica membranes and how it could be washed off later on?

I am doing DNA Extraction and Purification using silica based extraction kits. The companies can't tell me how much EDTA might be left in the purified DNA. First you bind the DNA to the silica membrane after that you wash with a mixture of ethanol and water, in the last step you elute in pure water.

I think that there should be no EDTA whatsoever left.

Some help is really appreciated here.

Thanks

Andreas

Hi,

Dose and one knows why Disodium EDTA precipitate Avicel RC 591 in the water media ? how can we avoid this precipitation ?