Eriochrome Black T
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
[Sodium 1-(1-hydroxy-2-naphthylazo)5-nitro-2-naphthol-4-sulfonate], C20H12N3NaO7S—461.38 [1787-61-7] —Brownish-black powder having a faint, metallic sheen. Soluble in alcohol, in methanol, and in hot water.
Suitability as Complexometric Indicator pH 10 ammoniacal buffer: Transfer 90 g of ammonium chloride to a 500-mL volumetric flask containing 375 mL of ammonium hydroxide.
Dilute with water to volume.
Magnesium standard solution: Transfer 1.014 g of Magnesium sulfate to a 100-mL volumetric flask. Dissolve in and dilute with water to volume.
Dilute 10 mL of this solution with water to 1 L.This solution contains 0.01 mg of magnesium per milliliter.
Sample solution: Dissolve 0.1 g of eriochrome black T in 100 mL of water, warming if necessary.
Procedure: In a suitable container, add 10 mL of pH 10 ammoniacal buffer to 100 mL of water. Add 0.5 mL of the Sample solution and 10.0 mL of Magnesium standard solution.
Acceptance criteria: The reagent meets the criteria for its use as a complexometric indicator if the color of the resulting solution is red-violet, and if turns into blue after the addition of 0.10 mL of 0.1 M edetate disodium VS.
