K2S2O5 222.33

Disulfurous acid, dipotassium salt.
Dipotassium pyrosulfite [16731-55-8].

Packaging and storage— Preserve in well-fitted, tight containers, and avoid exposure to excessive heat.

Identification— A solution (1 in 20) responds to the tests for Potassium 191 and for Sulfite 191.

Iron 241— Dissolve 1.00 g in 14 mL of dilute hydrochloric acid (2 in 7), and evaporate on a steam bath to dryness. Dissolve the residue in 7 mL of dilute hydrochloric acid (2 in 7), and again evaporate to dryness. Dissolve the resulting residue in a mixture of 2 mL of hydrochloric acid and 20 mL of water, add 3 drops of bromine TS, and boil to expel the bromine. Cool, and dilute with water to 47 mL: the limit is 0.001%.

Heavy metals, Method I 231— Dissolve 2 g in 20 mL of water, add 5 mL of hydrochloric acid, evaporate on a steam bath to about 1 mL, and dissolve the residue in 25 mL of water: the limit is 0.001%.

Assay— Transfer about 250 mg of Potassium Metabisulfite, accurately weighed, to a glass-stoppered conical flask containing 50.0 mL of 0.1 N iodine VS, and swirl to dissolve. Allow to stand for 5 minutes, protected from light, add 1 mL of hydrochloric acid, and titrate the excess iodine with 0.1 N sodium thiosulfate VS, adding 3 mL of starch TS as the endpoint is approached. Each mL of 0.1 N iodine is equivalent to 3.203 mg of SO2.

Topic/Question	Contact	Expert Committee
Monograph	Robert H. Lafaver, B.A. Scientist 1-301-816-8335	(EM105) Excipient Monographs 1

USP32–NF27 Page 1322

POTASSIUM METABISULFITE

Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.