De-ionised water & EDTA questions

Sonya-m · Jun 10, 2015

Is de-ionised the same as distilled?

I'm sure I read the usage rate for EDTA is 0.5% total oil weight but can someone confirm? I remember you can make a 39% solution in advance but it's the end quantity I can't remember

DeeAnna · Jun 10, 2015

The EDTA dosage can range from 0.2% to 4% of EDTA powder. The amount depends on what you want to do. Use 0.2% to 0.5% to chelate metal ions for longer shelf life (aka less chance of DOS). Use 0.5% to 4% to reduce hard water scum.

Most people on SMF use 0.5% of EDTA powder based on total fat weight, especially if they're adding EDTA to bar (NaOH) soap. This seems to work pretty well and is pretty much the soapers' usual way of figuring additives. Others (Irish Lass) base their dosage on the total batch weight. This method is easy to use when adding EDTA to diluted liquid soap AND this method more closely follows the manufacturer's recommendations, so you could use it for bar soap as well.

Even though you get different answers with the two methods, EDTA seems to be effective despite this variation in dosage. If you use total fat weight to calcuate the EDTA and you're not getting the results you want at 0.5%, try increasing the percentage a bit -- say 0.75% or 1% -- but don't go overboard. I can speak from experience that even higher rates of EDTA (3-4%) can be troublesome to use in CP soap and I really don't see a benefit to the higher amounts, so I suggest sticking with a lower dosage however you want to calculate it.

Irish Lass recommends dissolving EDTA in water to make a 39% solution by weight. This would be a mixture of 39 grams of EDTA powder with enough warm distilled water added to make a total of 100 grams of solution.

Be sure to use TETRAsodium EDTA, not DIsodium EDTA. TETRA is for alkaline products like soap and DI is for neutral to acidic products.

Here's how I calculate how much 39% solution to add, based on total batch weight:
Weight of 39% EDTA solution = (% EDTA powder in the soap) X (Total batch weight) / 39

Example 1: The total batch weight is 1000 grams and I want 0.5% EDTA in the recipe. The weight of EDTA solution is:
Weight 39% EDTA solution = (0.5) X (1000 grams) / 39 = 12.8 grams

Example 2: The total batch weight is 16 ounces and I want 0.5% EDTA in the recipe. The weight of EDTA solution is:
Weight 39% EDTA solution = (0.5) X (16 ounces) / 39 = 0.21 ounces

Irish Lass explains the math differently, but she and I end up in the exact same place.

Note: The Lotioncrafter EDTA powder I'm using is 83% to 85% pure. If you're using EDTA powder with a greatly different purity, you might want to take that into account. Just a few percent difference is not a big deal, however -- just use the same formulas that Irish Lass or I are using.

DeeAnna · Jun 10, 2015

Oh, forgot ... deionized is technically not the same as distilled, but good quality deionized water approaches the quality of distilled. I know distilled can be ridiculously expensive in some places, so I'd certainly used deionized if it was easier to get and/or cheaper than distilled.

IrishLass · Jun 10, 2015

Yep- like DeeAnna said, I like to work from a 39% solution of tetrasodium EDTA. I like to use it at .5% of my total batch weight, including the weight of my water and lye and all my additives, etc. I don't know what % that works out to be if based on just the oils, but for what it's worth, .5% of my entire batch weight is plenty enough EDTA to increase my lather in my hard water and to also cut down on scum. It hasn't cut the scum out completely, but it has definitely put a dent in it, and when I use my soap in the shower, it almost feels like I'm washing with soft water in the way the soap rinses off my skin. It's really nice- plus it has the added benefit of keeping DOS at bay.

Also- like DeeAnna explained, I do my math differently to figure out how much 39% tetrasodium EDTA to add to my batch (I learned it from someone over at the Dish and it's what I've gotten used to). For what it's worth, here is the 2-part equation that I do:

1) The total weight of my soap batch (in grams) X .5% = how much powdered EDTA is required for my batch.
2) The amount of powdered EDTA required for my batch X 2.56 = how much of my 39% solution to weigh out for my batch.

IrishLass

Sonya-m · Jun 10, 2015

This is why I love this place!! Thank you both for such informative answers!!

So after running my recipe through soapcalc if, for example, my total weight of everything came to 1000g I would use just 5g EDTA?

This is the one I have, do I need to be concerned it states 86% in the title? Should I increase to 5.8g to account for it?

DeeAnna · Jun 10, 2015

"...I like to use it at .5% of my total batch weight, including the weight of my water and lye and all my additives, etc...."

Yes, Irish Lass, I agree -- now that I've finally got my head in the game and am thinking about this correctly. This method follows the supplier's instructions.

I think some people use the % based on fat weight when they are calculating EDTA for use in bar (NaOH) soap because that seems to be a traditional soapers' way of doing things. This would give a lighter dose of EDTA compared with basing it on total batch weight. That means you might need to use a slightly higher % of EDTA based on fat weight to get the same results as if you based on the total batch weight. I'd still start at 0.5% of total fat weight and see how that works -- it might be fine.

"...my total weight of everything came to 1000g I would use just 5g EDTA?..."

Yep, that's right.

"...do I need to be concerned it states 86% in the title?..."

Um, in what title? Could you please clarify?

Sonya-m · Jun 11, 2015

Oops I didn't add the link to the one I got!!

http://m.ebay.co.uk/itm/261820309045?nav=SEARCH

DeeAnna · Jun 11, 2015

Okay, I understand you now. Thanks!

I've been using EDTA from Lotioncrafter. I went back and read through the info more carefully, and I now have egg on my face. The EDTA I'm using is 83% to 85% pure, pretty much the same as yours. The balance is water. I doublechecked the usage rates and they are meant for the actual product as sold (~85% pure), so the advice given in earlier posts in this thread is correct for your EDTA as well as mine.

Short answer -- Yes, stick with the 5 g of EDTA per 1000 g total weight, Sonya. You don't need to adjust for the purity.

DeeAnna · Jun 11, 2015

I've revised my answers in posts 2 and 6 -- please re-read. I needed to correct some of the things I originally wrote. My head's definitely not in the game -- I'm sorry for the confusion....

Saponista · Jun 12, 2015

In my experience, edta will only go into solution at a pH if 8 or over. If you try to dissolve it in water you will just end up with a precipitate. I have seen many newbie lab techs try to make this without success. As soon as you start adding some naoh to bring the pH up it starts to dissolve. So if you want to make a solution before hand, it's going to have to be a slightly alkaline one.

Sonya-m · Jun 12, 2015

I didn't have time to make a solution last night so just added it to my water before my lye, seemed to be ok

Saponista · Jun 12, 2015

Perhaps it will dissolve at the lower pH in the small quantities you are using.

DeeAnna · Jun 12, 2015

Saponista, I have to say I had zero problems making solutions of tetrasodium EDTA and warmed distilled water. The EDTA powder dissolved quickly and easily and has remained fully in solution since then. I made about 220 grams of solution each time, so, yes, it was only a small amount. If I do have trouble in the future, however, I'll keep your tip in mind.

Saponista · Jun 12, 2015

Ok perhaps it is only when you are making the higher molarity solutions.

DeeAnna · Jun 12, 2015

I didn't find any solubility tables in a quick search of the 'net, but I did find this info from Sigma Aldrich:

Tetrasodium EDTA: This product is soluble in water at room temperature up
to 1.45 M, which is ~550 mg in a final volume of 1 ml.
The pH of this solution will be 10 to 11 and will be
rather viscous. EDTA salts are more soluble in water as
the pH increases: the more EDTA there is in the salt
form, the higher the pH of a water solution, and
therefore, the higher the room temperature solubility
A stock solution of 0.5 M at pH 8.5 may be stored for
months at 4 °C without degradation.1

Disodium EDTA: This product is slowly soluble in water at room
temperature up to 0.26 M, which is approximately
96 mg in a final volume of 1 ml. The pH of this
solution will be in the range of 4 to 6. EDTA salts are
more soluble in water as the pH increases: the more
EDTA there is in the salt form, the higher the pH of a
water solution, and therefore, the higher the room
temperature solubility. This can be achieved by a
gradual addition of concentrated sodium hydroxide
solution to the EDTA solution. A stock solution of 0.5 M at
pH 8.5 is stable for months at 4 °C.

From this info, it looks like Tetra EDTA is quite a bit more soluble in water than Di. At a 39% w/w solution of Tetra and water per Irish Lass, we're making about a 1 M solution, if I'm doing the math correctly, so the molarity is fairly high although the solution is well below saturation.

On the other hand, this info shows Di EDTA is tough to dissolve and has a low saturation concentration in plain water. If you're using Di ETDA rather than Tetra, I can see why your experience and ours might be quite different!

Saponista · Jun 12, 2015

It must be the disodium that I am thinking of then.

not_ally · Jun 12, 2015

Definitely the di, Saponista, I make up 16 oz. squeeze bottles of the tri at 39% (thanks IL and DeeAnna) and use it all my batches, it dissolves pretty easily and stays suspended. Thank goodness, I need it for the chelation.

topofmurrayhill · Jun 12, 2015

Aren't those usage rate suggestions from Lotioncrafter a little (very) high? The Dunn experiments used 0.1% for stabilization. Dow Chemical suggests 0.1% to 0.2% for bar soaps. Those rates seem more typical.

hozhed · Jun 13, 2015

DeeAnna said:
The EDTA dosage can range from 0.2% to 4% of EDTA powder. The amount depends on what you want to do. Use 0.2% to 0.5% to chelate metal ions for longer shelf life (aka less chance of DOS). Use 0.5% to 4% to reduce hard water scum.

Most people on SMF use 0.5% of EDTA powder based on total fat weight, especially if they're adding EDTA to bar (NaOH) soap. This seems to work pretty well and is pretty much the soapers' usual way of figuring additives. Others (Irish Lass) base their dosage on the total batch weight. This method is easy to use when adding EDTA to diluted liquid soap AND this method more closely follows the manufacturer's recommendations, so you could use it for bar soap as well.

Even though you get different answers with the two methods, EDTA seems to be effective despite this variation in dosage. If you use total fat weight to calcuate the EDTA and you're not getting the results you want at 0.5%, try increasing the percentage a bit -- say 0.75% or 1% -- but don't go overboard. I can speak from experience that even higher rates of EDTA (3-4%) can be troublesome to use in CP soap and I really don't see a benefit to the higher amounts, so I suggest sticking with a lower dosage however you want to calculate it.

Irish Lass recommends dissolving EDTA in water to make a 39% solution by weight. This would be a mixture of 39 grams of EDTA powder with enough warm distilled water added to make a total of 100 grams of solution.

Be sure to use TETRAsodium EDTA, not DIsodium EDTA. TETRA is for alkaline products like soap and DI is for neutral to acidic products.

Here's how I calculate how much 39% solution to add, based on total batch weight:
Weight of 39% EDTA solution = (% EDTA powder in the soap) X (Total batch weight) / 39

Example 1: The total batch weight is 1000 grams and I want 0.5% EDTA in the recipe. The weight of EDTA solution is:
Weight 39% EDTA solution = (0.5) X (1000 grams) / 39 = 12.8 grams

Example 2: The total batch weight is 16 ounces and I want 0.5% EDTA in the recipe. The weight of EDTA solution is:
Weight 39% EDTA solution = (0.5) X (16 ounces) / 39 = 0.21 ounces

Irish Lass explains the math differently, but she and I end up in the exact same place.

Note: The Lotioncrafter EDTA powder I'm using is 83% to 85% pure. If you're using EDTA powder with a greatly different purity, you might want to take that into account. Just a few percent difference is not a big deal, however -- just use the same formulas that Irish Lass or I are using.

DeeAnna......why use a chelant for soap if you use distilled water? Where are the metals coming from? thanks

Sonya-m · Jun 13, 2015

They're coming from the water you bathe/shower in.

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