Packaging and storage—
Preserve in tight, light-resistant containers. Store at 25
, excursions permitted between 15
and 30
.
Identification—
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.
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 C
16H
8N
2Na
2O
8S
2 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.
;)
