Phosphoric Acid
H3PO4 98.00

Phosphoric acid.
Phosphoric acid [7664-38-2].
» Phosphoric Acid contains not less than 85.0 percent and not more than 88.0 percent, by weight, of H3PO4.
Caution—Avoid contact, as Phosphoric Acid rapidly destroys tissues.
Packaging and storage— Preserve in tight containers.
Identification— When carefully neutralized with 1 N sodium hydroxide, phenolphthalein TS being used as the indicator, it responds to the tests for Phosphate 191.
Sulfate 221 Dilute 6 mL of Phosphoric Acid with 90 mL of water, and add 1 mL of barium chloride TS: no precipitate is formed immediately.
Alkali phosphates— Transfer 1 mL of it to a graduated cylinder, and add 6 mL of ether and 2 mL of alcohol: no turbidity is produced.
Limit of nitrate— Dilute 6 mL of Phosphoric Acid with 14 mL of water, mix 5 mL of the dilution with about 0.1 mL of indigo carmine TS, then add 5 mL of sulfuric acid: the blue color is not discharged within 1 minute.
Phosphorous or hypophosphorous acid— Dilute 6 mL of Phosphoric Acid with 14 mL of water. Gently warm 5 mL of the dilution, and add 2 mL of silver nitrate TS: the mixture does not become brownish.
Assay— Weigh accurately about 1 g of Phosphoric Acid in a tared, glass-stoppered flask, and dilute it with water to about 120 mL. Add 0.5 mL of thymolphthalein TS, and titrate with 1 N sodium hydroxide VS to the first appearance of a blue color. Perform a blank determination, and make any necessary correction. Each mL of 1 N sodium hydroxide is equivalent to 49.00 mg of H3PO4.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Robert H. Lafaver, B.A.
(EM105) Excipient Monographs 1
USP32–NF27 Page 1301
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.