How to Make EDTA Solution


EDTA isn't soluble in water unless the pH is at least 8, so you need to add NaOH to make EDTA solution.
EDTA isn’t soluble in water unless the pH is at least 8, so you need to add NaOH to make EDTA solution.

EDTA is the acronym for ethylenediamine tetraacetic acid. EDTA finds use as a ligand and chelating agent. In the lab, it’s used to sequester calcium (Ca2+) and iron (Fe3+) metal ions. In medicine, it’s used to treat lead poisoning, hypercalcemia, and ventricular arrhythmia. Here is how to prepare a 0.5M ETDA stock solution and recipes for other EDTA solutions.

EDTA Solution Ingredients

The free form of EDTA is essentially insoluble in water, so prepare EDTA solution using disodium EDTA. Even then, the solid won’t dissolve until the solution reaches pH 8.0, so you’ll need sodium hydroxide pellets or stock solution. To make 0.5M EDTA stock solution, you need:

  • 186.1 grams EDTA (disodium ethylenediaminetetraacetate•2H2O) 
  • 800 milliliters distilled water
  • Sodium hydroxide (NaOH) solution or solid (to adjust pH)

Procedure

  1. Stir 186.1 g disodium ethylenediaminetetraacetate•2H2O into 800 ml of distilled water.
  2. Stir the solution vigorously using a magnetic stirrer.
  3. Add NaOH to adjust the pH to 8.0. You may be surprised how much sodium hydroxide you need to add to raise the pH enough to dissolve the EDTA. If you use solid NaOH pellets, you’ll need 18 to 20 grams of NaOH. Add the last of the NaOH slowly so that you don’t overshoot the pH. You may wish to switch from solid NaOH to a solution toward the end for more precise control. The EDTA will slowly go into solution as the pH nears 8.0.
  4. Dilute the solution to 1 L with distilled water.
  5. Filter the solution through a 0.5-micron filter.
  6. Dispense into containers as needed and sterilize in an autoclave. The resulting solution should be clear and colorless.
  7. 0.5M EDTA solution is stable for 1 year when stored at 4°C .

Other Common EDTA Recipes

The point of making a stock solution is so you can dilute it to make other solutions. However, if you commonly use a certain concentration, you can make it directly. The procedure is the same. Mix the disodium EDTA with water, use NaOH to get it to dissolve, and then add distilled water to reach the final volume.

0.02 N EDTA

  • 3.732 g disodium EDTA
  • 1 liter water
  • NaOH pellets or solution

0.1 M EDTA

  • 37.2 g disodium EDTA
  • 1 liter water
  • NaOH

100 mL 0.5M EDTA

  • 18.61 g disodium EDTA
  • 100 mL water
  • NaOH

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