EDTA at pH 4-4.5 - Chemists Corner

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EDTA at pH 4-4.5

Posted by Abdullah on December 13, 2021 at 1:26 pm

I am currently using EDTA in shampoo and lotion at 0.2% and the pH of both products are 4-4.5. as at pH 4-4.5 EDTA is less effective, which plan is better?

1. Increase the amount of EDTA to compensate the less effectiveness

2. Reduce it or remove it because at pH 4-4.5 EDTA doesn’t do much no matter how much i add

Abdullah replied 2 years, 11 months ago 6 Members · 13 Replies
13 Replies

chemicalmatt

Member
December 13, 2021 at 10:47 pm

Disodium EDTA has a decently good formation constant for Fe++ in that pH range. Tetrasodium EDTA does not.
Abdullah

Member
December 14, 2021 at 1:52 am

@chemicalmatt unfortunately i use and have only tetrasodium EDTA available.

Is it the EDTA part that chelates iron or the sodium part? I mean the only difference is that tetrasodium has two more sodium to make it more water soluble. Is these other different?
So what is causing tetrasodium EDTA not chelate iron at pH 4?
Mayday

Member
December 18, 2021 at 9:10 am

Abdullah said:

So what is causing tetrasodium EDTA not chelate iron at pH 4?

Hi again @Abdullah ????

I can’t answer the chemistry question, but I have found a reference to the fact that each EDTA has their own pH at a standard 5% aqueous solution. They referenced the British Pharmacopoiea, which I do not have access to currently. My guess is that the pH of the EDTA corresponds to the pH range it is effective in.

I could be wrong, but the range for tEDTA (8.5-10) tracks with how I’ve seen it recommended for use in alkaline solutions, soaps, etc. So for yours you should use Disodium EDTA. Can also consider Sodium Phytate or Tetrasodium Glutamate Diacetate, as I believe those are effective at low pH.
Abdullah

Member
December 18, 2021 at 10:29 am

Mayday said:

Abdullah said:

So what is causing tetrasodium EDTA not chelate iron at pH 4?

Hi again @Abdullah ????

I can’t answer the chemistry question, but I have found a reference to the fact that each EDTA has their own pH at a standard 5% aqueous solution. They referenced the British Pharmacopoiea, which I do not have access to currently. My guess is that the pH of the EDTA corresponds to the pH range it is effective in.

I could be wrong, but the range for tEDTA (8.5-10) tracks with how I’ve seen it recommended for use in alkaline solutions, soaps, etc. So for yours you should use Disodium EDTA. Can also consider Sodium Phytate or Tetrasodium Glutamate Diacetate, as I believe those are effective at low pH.

Thanks
Mayday

Member
December 18, 2021 at 11:33 pm

@Abdullah Warning that sodium phytate will probably need more pH adjustment then disodium EDTA. At 0.05% NaPhy, 0.35% NaBenz, I needed 0.20% citrate to get to pH 4.4 from 10.9
Mayday

Member
December 19, 2021 at 12:06 am

(On second thought that may actually be the NaBenz)
Abdullah

Member
December 19, 2021 at 1:55 am

Mayday said:

@Abdullah Warning that sodium phytate will probably need more pH adjustment then disodium EDTA. At 0.05% NaPhy, 0.35% NaBenz, I needed 0.20% citrate to get to pH 4.4 from 10.9

Of course i will adjust the pH no matter what i use.

Sodium phytate is expensive and i am selling low price products.
Mayday

Member
December 19, 2021 at 2:30 am

Abdullah said:
[…]Sodium phytate is expensive and i am selling low price products.

Considering citric acid is cheap and you already have it in your formula, have you considered chelating with it? Would have to adjust pH down, but it sounds possible. And IDK how it would fare compared to dEDTA.
Abdullah

Member
December 19, 2021 at 3:49 am

Mayday said:

Abdullah said:
[…]Sodium phytate is expensive and i am selling low price products.

Considering citric acid is cheap and you already have it in your formula, have you considered chelating with it? Would have to adjust pH down, but it sounds possible. And IDK how it would fare compared to dEDTA.

It is much weaker than EDTA. Like more than hundred times.
ketchito

Member
December 20, 2021 at 12:37 pm

Abdullah said:

@chemicalmatt unfortunately i use and have only tetrasodium EDTA available.

Is it the EDTA part that chelates iron or the sodium part? I mean the only difference is that tetrasodium has two more sodium to make it more water soluble. Is these other different?
So what is causing tetrasodium EDTA not chelate iron at pH 4?

It’s the carboxylic groups in EDTA the ones that bind cations (iron in solution would have positive charge, same as sodium, and it’ll make them repel). But when you lower the pH, the carboxylic groups get protonated and unavailable to bind cations.
PhilGeis

Member
December 20, 2021 at 5:59 pm

https://study.com/academy/answer/edta-is-a-hexaprotic-system-with-the-following-pka-values-pka1-0-00-pka2-1-50-pka3-2-00-pka4-2-69-pka5-6-13-pka6-10-37-the-distribution-of-protonated-forms-of-edta-will-therefore-vary-wi.html
ngarayeva001

Member
December 21, 2021 at 1:30 am

A bit off topic but I thought someone might find it useful, surfactant Iselux https://www.ulprospector.com/en/eu/PersonalCare/Detail/3904/97777/Iselux
requires chelator to clarify (otherwise it’s cloudy). Citric acid is sufficient for this purpose.
Citric acid is a super versatile ingredient.
Abdullah

Member
December 21, 2021 at 4:09 am

Thank you all