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].

Packaging and storage— Preserve in tight,light-resistant containers.Store at 25,excursions permitted between 15and 30.

USP Reference standards á11ñ— USP Indigotindisulfonate Sodium RS.

Identification—

Loss on drying á731ñ— Dry it at 105for 3hours:it loses not more than 5.0%of its weight.

Water-insoluble substances— Dissolve 1.0g in 100mLof water,pass through a tared filtering crucible,wash with water until the filtrate is practically colorless,and dry the residue at 105for 1hour:the weight of the residue does not exceed 5mg.

Arsenic,Method IIá211ñ: 8ppm.

Lead— Place 4.0g in a Kjeldahl flask,moisten with water,and add 10mLof sulfuric acid and 5mLof 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,1to 3mLat 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,5mLof 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 10to 20minutes after the addition of the perchloric acid,add 1to 3mLmore of this acid,and continue the nitric acid treatment until the solution is colorless.)Boil for 10to 15minutes,cool,and neutralize with 1Nsodium hydroxide.Transfer to a 100-mLvolumetric flask,and dilute with water to volume.Five mLof this solution contains not more than 2µg of lead (corresponding to not more than 0.001%)when tested according to the limit test for Lead á251ñ,3mLof Ammonium Citrate Solution,1mLof Potassium Cyanide Solution,and 0.5mLof Hydroxylamine Hydrochloride Solutionbeing used.

Sulfur content— Place about 25mg,accurately weighed,in halide-free filter paper measuring about 4cm square,and fold the paper to enclose it.Proceed as directed under Oxygen Flask Combustion á471ñ,using a 1-Lflask and using a mixture of 25mLof water and 5mLof hydrogen peroxide TSas the absorbing liquid.When the combustion is complete,place a few mLof water in the cup,loosen the stopper,then rinse the stopper,the specimen holder,and the sides of the flask with about 20mLof water.Add 2mLof hydrochloric acid,dilute with water to 250mL,heat to boiling,and slowly add 10mLof barium chloride TS.Heat the mixture on a steam bath for 1hour,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 137.4mg of sulfur (S).Between 13.0%and 14.0%,calculated on the dried basis,of Sis found.

Assay— Dissolve about 500mg of Indigotindisulfonate Sodium,accurately weighed,in dilute hydrochloric acid (1in 100),and dilute quantitatively and stepwise with the dilute acid to obtain a solution containing about 10µg per mL.Concomitantly determine the absorbances of this solution and a Standard solution of USP Indigotindisulfonate Sodium RSin the same medium having a known concentration of about 10µg per mL,in 1-cm cells at the wavelength of maximum absorbance at about 610nm,with a suitable spectrophotometer,using dilute hydrochloric acid (1in 100)as the blank.Calculate the quantity,in mg,of C16H8N2Na2O8S2in the portion of Indigotindisulfonate Sodium taken by the formula: in which Cis the concentration,in µg per mL,of USP Indigotindisulfonate Sodium RSin the Standard solution;and AUand ASare the absorbances of the solution of Indigotindisulfonate Sodium and the Standard solution,respectively.

Expert Committee:(GTB)General Toxicology and Biocompatibility

USP28–NF23Page 1007

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