Preparation and standardization of 0.05 M Disodium Edetate USP Volumetric Solution

1.  PREPARATION:

Dissolve 18.6 g of Disodium Edetate in water to make 1000 mL.

2. STANDARDIZATION :

A) Standardization with visual endpoint :

Accurately weigh about 200 mg of chelometric standard Calcium carbonate, previously dried at 210°C for 4 hours and cooled in a desiccator, transfer to a 400 mL beaker, add 10 mL of water, and swirl to form a slurry. Cover the beaker with a watch glass, and introduce 2 mL of diluted Hydrochloric acid from a pipette inserted between the lip of the beaker and the edge of the watch glass. Swirl the contents of the beaker to dissolve the Calcium carbonate. Wash down the sides of the beaker, the outer surface of the pipette, and the watch glass with water, and dilute with water to about 100 mL. While stirring the solution, preferably with a magnetic stirrer, add about 30 mL of the  Disodium Edetate solution from a 50 mL burette. Adjust the solution to a pH of 12–13 with sodium hydroxide TS, add 300 mg of hydroxy naphthol blue, and continue the titration with the edetate disodium solution to a blue endpoint.

Calculation:

          Molarity (M) = [Weight of Calcium carbonate (in g) x (Assay/100) x 1000]/ [100.09 x Volume of 0.05 M Disodium Edetate consumed (in mL)]

B) Standardization with potentiometric endpoint :

Accurately weigh about 100 mg of chelometric standard calcium carbonate, previously dried at 210° for 4 h and cooled in a desiccator, transfer to a 400-mL beaker, add 10 mL of water, and swirl to form a slurry. Cover the beaker with a watch glass, and introduce 1 mL of diluted hydrochloric acid from a pipette inserted between the lip of the beaker and the edge of the watch glass. Swirl the contents of the beaker to dissolve the calcium carbonate. Wash down the sides of the beaker, the outer surface of the pipet, and the watch glass with water, and dilute with water to about 100 mL. Adjust the solution to a pH of 12–13 with sodium hydroxide TS and titrate potentiometrically with the edetate disodium solution using a combined calcium ion-selective electrode.

Calculation:

Molarity (M) = [Weight of Calcium carbonate (in g) x (Assay/100) x 1000]/ [100.09  x Volume of 0.05 M Disodium Edetate consumed (in mL)]                          

Limit: 0.05 M ± 5 % (0.0475 M – 0.0525 M)

3. PREPARATION OF INDICATORS / REAGENTS:

a. Diluted Hydrochloric acid:

Dilute 22.6 mL Hydrochloric acid to 100 mL with water.

b. Sodium hydroxide TS:

Dissolve 4.0 g of Sodium hydroxide in water to make 100 mL.

4. STORAGE CONDITION:

Store in glass stoppered bottles.