Diluted Phosphoric Acid
» Diluted Phosphoric Acid contains, in each 100 mL, not less than 9.5 g and not more than 10.5 g of H3PO4.
Diluted Phosphoric Acid may be prepared as follows:
Phosphoric Acid 69 mL
Purified Water, a sufficient quantity, to make 1000 mL
Mix the ingredients.
Packaging and storage— Preserve in tight containers.
Heavy metals, Method I 231 Dilute 10 g (9.5 mL) with 10 mL of water, add 6 mL of 1 N sodium hydroxide, and dilute with water to 50 mL. Dilute 20 mL of this solution with water to 25 mL: the limit is 5 ppm.
Alkali phosphates— Evaporate 20 mL on a steam bath to a weight of about 5 g. Cool, transfer 2 mL to a graduated cylinder, and add 6 mL of ether and 2 mL of alcohol: no turbidity is produced.
Other tests— Without further dilution, 100 mL of Diluted Phosphoric Acid responds to the Identification test and meets the requirements of the tests for Nitrate, Phosphorous or hypophosphorous acid, and Sulfate under Phosphoric Acid.
Assay— Transfer 10.0 mL of Diluted Phosphoric Acid to a flask, and dilute it with water to about 50 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, M.S.
Scientific Liaison
(EXC2010) Monographs - Excipients
USP35–NF30 Page 1891