Indigotindisulfonate Sodium
(in'' di goe'' tin dye sul' foe nate soe' dee um).
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C16H8N2Na2O8S2 466.35

1H-Indole-5-sulfonic acid,2-(1,3-dihydro-3-oxo-5-sulfo-2H-indol-2-ylidene)-2,3-dihydro-3-oxo-, disodium salt.
Disodium 3,3¢-dioxo[D2,2¢-biindoline]-5,5¢-disulfonate [860-22-0].
» Indigotindisulfonate Sodium contains not less than 96.0 percent and not more than 102.0 percent of sodium indigotinsulfonates, calculated on the dried basis as C16H8N2Na2O8S2.
Packaging and storage— Preserve in tight, light-resistant containers. Store at 25, excursions permitted between 15 and 30.
USP Reference standards 11
USP Indigotindisulfonate Sodium RS Click to View Structure
Identification—
A: Incinerate a portion of it: the residue responds to the tests for Sodium 191 and for Sulfate 191.
B: The addition of hydrochloric acid to a solution of it changes the color to bluish violet, and further dilution with water restores the original color.
C: The addition of 1 N sodium hydroxide to a solution of it changes the color to yellow or olive-brown.
D: The addition of sodium chloride to a solution of it produces a blue precipitate.
Loss on drying 731 Dry it at 105 for 3 hours: it loses not more than 5.0% of its weight.
Water-insoluble substances— Dissolve 1.0 g in 100 mL of water, pass through a tared filtering crucible, wash with water until the filtrate is practically colorless, and dry the residue at 105 for 1 hour: the weight of the residue does not exceed 5 mg.
Lead— Place 4.0 g in a Kjeldahl flask, moisten with water, and add 10 mL of sulfuric acid and 5 mL of nitric acid. As soon as the first violent reaction subsides, heat until most of the brown fumes are expelled. Repeat the addition of nitric acid, 1 to 3 mL at a time, and heat until the Indigotindisulfonate Sodium is practically decomposed and most of the organic matter is in solution. Then add, cautiously and in small portions, 5 mL of perchloric acid. When the violent reaction subsides, continue the addition of small amounts of nitric acid, and heat as before until a colorless solution is obtained. (If the solution fails to become clear in 10 to 20 minutes after the addition of the perchloric acid, add 1 to 3 mL more of this acid, and continue the nitric acid treatment until the solution is colorless.) Boil for 10 to 15 minutes, cool, and neutralize with 1 N sodium hydroxide. Transfer to a 100-mL volumetric flask, and dilute with water to volume. Five mL of this solution contains not more than 2 µg of lead (corresponding to not more than 0.001%) when tested according to the limit test for Lead 251, 3 mL of Ammonium Citrate Solution, 1 mL of Potassium Cyanide Solution, and 0.5 mL of Hydroxylamine Hydrochloride Solution being used.
Sulfur content— Place about 25 mg, accurately weighed, in halide-free filter paper measuring about 4 cm square, and fold the paper to enclose it. Proceed as directed under Oxygen Flask Combustion 471, using a 1-L flask and using a mixture of 25 mL of water and 5 mL of hydrogen peroxide TS as the absorbing liquid. When the combustion is complete, place a few mL of water in the cup, loosen the stopper, then rinse the stopper, the specimen holder, and the sides of the flask with about 20 mL of water. Add 2 mL of hydrochloric acid, dilute with water to 250 mL, heat to boiling, and slowly add 10 mL of barium chloride TS. Heat the mixture on a steam bath for 1 hour, collect the precipitate of barium sulfate on a filter, wash it until free from chloride, dry, ignite, and weigh. Each g of residue is equivalent to 137.4 mg of sulfur (S). Between 13.0% and 14.0%, calculated on the dried basis, of S is found.
Assay— Dissolve about 500 mg of Indigotindisulfonate Sodium, accurately weighed, in dilute hydrochloric acid (1 in 100), and dilute quantitatively and stepwise with the dilute acid to obtain a solution containing about 10 µg per mL. Concomitantly determine the absorbances of this solution and a Standard solution of USP Indigotindisulfonate Sodium RS in the same medium having a known concentration of about 10 µg per mL, in 1-cm cells at the wavelength of maximum absorbance at about 610 nm, with a suitable spectrophotometer, using dilute hydrochloric acid (1 in 100) as the blank. Calculate the quantity, in mg, of C16H8N2Na2O8S2 in the portion of Indigotindisulfonate Sodium taken by the formula:
50C(AU / AS)
in which C is the concentration, in µg per mL, of USP Indigotindisulfonate Sodium RS in the Standard solution; and AU and AS are the absorbances of the solution of Indigotindisulfonate Sodium and the Standard solution, respectively.
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USP35–NF30 Page 3488
Pharmacopeial Forum: Volume No. 29(6) Page 1905