Packaging and storage—
Preserve in tight containers.
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.
