Molecular formula. C₁₀H₁₂CaN₂Na₂O₈,2H₂O

Relative molecular mass. 410.3

Graphic formula.

Chemical name. Disodium [(ethylenedinitrilo)tetraacetato]calciate(2-) dihydrate; (OC-6-21)-disodium [[N,N'-1,2-ethanediylbis[N-(carboxymethyl)glycinato]](4-)-N,N',O,O',O^N,O^N']calciate(2-) dihydrate; calcium chelate of the disodium salt of ethylenediamine-N,N,N',N'-tetraacetic acid dihydrate; CAS Reg. No. 6766-87-6 (dihydrate).

Description. A white or creamy white powder; almost odourless.

Solubility. Soluble in 2 parts of water; very slightly soluble in ethanol (~750 g/l) TS; practically insoluble in in ether R.

Category. Antidote, chelating agent for metals, mainly lead.

Storage. Sodium calcium edetate should be kept in a tightly closed container.

Additional information. Even in the absence of light, Sodium calcium edetate is gradually degraded on exposure to a humid atmosphere, the decomposition being faster at higher temperatures.

Requirements

Definition. Sodium calcium edetate contains not less than 97.0% and not more than 102.0% of C₁₀H₁₂CaN₂Na₂O₈, calculated with reference to the anhydrous substance.

Identity tests

A. Dissolve 2.0 g in 25 mL of water, add 2.0 mL of lead nitrate (100 g/l) TS, shake and add 6 mL of potassium iodide (80 g/l) TS; no yellow precipitate can be observed (keep the solution for test C).

B. To 0.15 mL of ferric chloride (25 g/l) TS add 0.15 mL of ammonium thiocyanate (75 g/l) TS; to this deep red-coloured solution add about 0.05 g of the test substance; the deep red colour changes to yellow.

C. To the solution prepared in test A, add ammonia (~100 g/l) TS, drop by drop, until an alkaline reaction is obtained with pH-indicator paper R. Add 5 mL of ammonium oxalate (25 g/l) TS; a white precipitate is produced (distinction from disodium edetate).

D. When tested for sodium as described under 2.1 General identification tests, yields the characteristic reactions. If reaction B is to be used, ignite a small quantity and dissolve the residue in acetic acid (~60 g/l) TS.

Heavy metals. Use 1.0 g for the preparation of the test solution as described under 2.2.3 Limit test for heavy metals, Procedure 3; determine the heavy metals content according to Method A; not more than 20 μg/g.

Cyanide. Dissolve 1.0 g in 50 mL of water, add 0.1 g of potassium iodide R, 4 mL of ammonia (~100 g/l) TS, and 0.10 mL of silver nitrate (0.01 mol/l) VS, and allow to stand for 1 minute; the opalescence produced is not less than that of a standard solution containing 1 mL of nitric acid (~130 g/l) TS, 1.0 mL of hydrochloric acid (0.0001 mol/l) VS, 9 mL of water, and 0.10 mL of silver nitrate (0.1 mol/l) VS, this solution having also been allowed to stand for 1 minute.

Disodium edetate. Dissolve 5.0 g in 20 mL of water, add 10 mL of ammonia buffer TS2 and 0.2 g of mordant black 11 indicator mixture R, and titrate with magnesium chloride (0.1 mol/l) VS. Not more than 1.5 mL of magnesium chloride (0.1 mol/l) VS is required.

Iron. Ignite 0.5 g and dissolve the residue in 40 mL of water. Treat the solution as described under 2.2.4 Limit test for iron; not more than 80 μg/g.

Water. Determine as described under 2.8 Determination of water by the Karl Fischer method, Method A, using about 0.2 g of the substance; the water content is not more than 130 mg/g.

pH value. pH of a 0.20 g/mL solution in carbon-dioxide-free water R, 6.5-8.0.

Assay. Dissolve about 0.5 g, accurately weighed, in 90 mL of water, add 7 g of methenamine R and 5 mL of hydrochloric acid (~70 g/l) TS. Titrate with lead nitrate (0.05 mol/l) VS, using xylenol orange indicator mixture R. Each mL of lead nitrate (0.05 mol/l) VS is equivalent to 18.71 mg of C₁₀H₁₂CaN₂Na₂O₈.

Additional requirements for Sodium calcium edetate for parenteral use

Complies with the monograph for "Parenteral preparations".

Bacterial endotoxins. Carry out the test as described under 3.4 Test for bacterial endotoxins; contains not more than 0.2 IU of endotoxin RS per mg of sodium edetate.