Hypophosphorous Acid
H3PO2 66.00

Phosphinic acid.
Hypophosphorous acid [6303-21-5].
» Hypophosphorous Acid contains not less than 30.0 percent and not more than 32.0 percent of H3PO2.
Packaging and storage— Preserve in tight containers.
Identification— It responds to the tests for Hypophosphite 191.
Limit of barium and oxalate—
Test solution— Dilute Hypophosphorous Acid with 3 volumes of water, and use this solution for the following tests.
Barium— Neutralize 30 mL of Test solution with 6 N ammonium hydroxide: the mixture exhibits little or no precipitation. Filter, acidify 10 mL of the filtrate with hydrochloric acid, and add 2 mL of potassium sulfate TS: no turbidity is produced.
Oxalate— Another 10-mL portion of the filtrate obtained in the test for Barium shows no turbidity upon the addition of 1 mL of calcium chloride TS.
Heavy metals, Method I 231 Place 0.90 mL (1 g) in a small beaker, and add 3 mL of water. Add 1 mL of nitric acid, and evaporate on a steam bath to about 1 mL. Again add 1 mL of nitric acid, and evaporate on a steam bath. Dissolve the residue in 3 mL of water, add 6 N ammonium hydroxide until the solution is distinctly alkaline to litmus, then boil gently until the odor of ammonia disappears. Add 2 mL of 1 N acetic acid and 15 mL of warm water, filter, and dilute the filtrate with water to 25 mL: the limit is 0.002%.
Assay— Pour about 7 mL of Hypophosphorous Acid into a tared, glass-stoppered flask, and weigh accurately. Dilute with about 25 mL of water, add phenolphthalein TS, and titrate with 1 N sodium hydroxide VS. Each mL of 1 N sodium hydroxide is equivalent to 66.00 mg of H3PO2.
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 1255
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.