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— Asolution (1in 20)responds to the tests for Potassium á191ñand for Sulfite á191ñ.

Iron á241ñ— Dissolve 1.00g in 14mLof dilute hydrochloric acid (2in 7),and evaporate on a steam bath to dryness.Dissolve the residue in 7mLof dilute hydrochloric acid (2in 7),and again evaporate to dryness.Dissolve the resulting residue in a mixture of 2mLof hydrochloric acid and 20mLof water,add 3drops of bromine TS,and boil to expel the bromine.Cool,and dilute with water to 47mL:the limit is 0.001%.

Heavy metals,Method Iá231ñ— Dissolve 2g in 20mLof water,add 5mLof hydrochloric acid,evaporate on a steam bath to about 1mL,and dissolve the residue in 25mLof water:the limit is 0.001%.

Organic volatile impurities,Method Vá467ñ: meets the requirements.

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

Expert Committee:(EMC)Excipients:Monograph Content

USP28–NF23Page 3065

Phone Number:1-301-816-8379