Disodium EDTA
Binds hard-water minerals, for less soap scum.
Opens the calculator’s starter recipe, 1000 g of oils, with this additive at the dose it fills in, ready to change.
What it is
Disodium EDTA is the disodium salt of EDTA, sold as its dihydrate, a powder of at least 99 % whose 1 % solution is acidic, pH 4 to 5. It is the form made for products at neutral pH.
How much
- 0.1–0.3 % of the batch in cosmetics generally filled in Lotioncrafter supplier or guide
- up to 0.25 % of the batch in rinse-off products, the highest reported use: not a recommendation CIR primary source
The calculator fills in 0.1 % of the batch: 1.4 g for the 1000 g of oils in its starter recipe.
When and how
- Usually: into the lye solution.
- Weigh it dry and dissolve it in the recipe’s own water: no extra water.
Classic Bells supplier or guide
What it does to the recipe
- Every 100 g takes 21.49 g of sodium hydroxide, which the calculator adds to the lye.
Nouryon primary source, Classic Bells supplier or guide, Stoichiometry primary source
Worth knowing
- In the lye it becomes tetrasodium EDTA, taking sodium hydroxide that the calculator adds to the lye. Dow sells the disodium form for neutral products and the tetrasodium form for bar soap. Dow primary source, Classic Bells supplier or guide
- No soap source gives a dose: the one here is for cosmetics in general.
Spoons and drops
- 1 tsp ≈ 2.96 g (2.46–3.45 g)
- 1 tbsp ≈ 8.87 g (7.39–10.4 g)
- 1 cup ≈ 142 g (118–166 g)
Nouryon primary source
INCI name
Disodium EDTA
- CAS number
- 139-33-3, 6381-92-6
- EC number
- 205-358-3
- In the finished bar
- with NaOH, Tetrasodium EDTA
Guides that discuss it
Sources
Nouryon, Dissolvine NA2 product data sheet (2022): disodium EDTA dihydrate, assay at least 99 %, pH 4.0–5.0 at 1 %, poured bulk density about 500–700 kg/m³.
Classic Bells, "EDTA": 0.05–0.25 % for rancidity; "Do not adjust your lye weight for EDTA"; disodium EDTA stirred into the lye becomes tetrasodium EDTA with "a small excess of NaOH", 22 g per 100 g (untested by the author).
Neutralisation stoichiometry with IUPAC 2013 molar masses: grams of NaOH per gram = protons × 39.997 ÷ molar mass. Disodium EDTA dihydrate (372.24 g/mol) takes 2; sodium bicarbonate (84.007 g/mol) 1; magnesium sulfate heptahydrate (246.47 g/mol) 2; borax decahydrate (381.37 g/mol) 2, to sodium metaborate; malic acid (134.087 g/mol) 2; citric acid (192.124 g/mol) 3. An acidity given in milliequivalents per litre takes that many millimoles of NaOH per litre.
Lotioncrafter, disodium EDTA: 0.1–0.3 % in cosmetics.
Cosmetic Ingredient Review, EDTA and its salts (2002): tetrasodium EDTA up to 0.56 % and disodium EDTA up to 0.25 % in bath soaps and detergents.
The highest concentration reported to CIR in industry surveys: what has been used, not a recommendation.
The Dow Chemical Company, VERSENE Chelating Agents (2007): in bar soap 0.1–0.2 %, where it "Helps prevent softening, brown-spotting, rancidity, cracking and discoloration due to metal ions"; disodium EDTA is "for use in products at neutral pH".