KH2PO4 136.09

Phosphoric acid,monopotassium salt.
Monopotassium phosphate [7778-77-0].

Packaging and storage— Preserve in tight containers.

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

Loss on drying á731ñ— Dry it at 105for 4hours:it loses not more than 1.0%of its weight.

Insoluble substances— Dissolve 10g in 100mLof hot water,filter through a tared filtering crucible,wash the insoluble residue with hot water,and dry at 105for 2hours:the residue does not exceed 20mg (0.2%).

Arsenic,Method Iá211ñ: 3ppm.

Lead— Asolution of 1g in 20mLof water contains not more than 5µg of lead (corresponding to not more than 5ppm of Pb)when tested as directed in the test for Lead á251ñ.

Heavy metals,Method Iá231ñ— Dissolve 1g in 25mLof water:the limit is 0.002%.

Limit of fluoride— Proceed as directed in the test for Fluorideunder Dibasic Calcium Phosphate.The limit is 0.001%.

Organic volatile impurities,Method Iá467ñ: meets the requirements.

Assay— Transfer about 5g of Monobasic Potassium Phosphate,previously dried and accurately weighed,to a 250-mLbeaker,add 100mLof water and 5.0mLof 1Nhydrochloric acid VS,and stir until the assay specimen is completely dissolved.Place the electrodes of a suitable pHmeter in the solution,and slowly titrate the excess acid,stirring constantly,with 1Nsodium hydroxide VSto the inflection point occurring at about pH4.Record the buret reading,and calculate the volume (A),if any,of 1Nhydrochloric acid consumed by the assay specimen.Continue the titration with 1Nsodium hydroxide VSuntil the inflection point occurring at about pH8.8is reached,record the buret reading,and calculate the volume (B)of 1Nsodium hydroxide required in the titration between the two inflection points (pH4and 8.8).Each mLof the volume (B-A)of 1Nsodium hydroxide is equivalent to 136.1mg of KH2PO4.

Expert Committee:(EMC)Excipients:Monograph Content

USP28–NF23Page 3066

Phone Number:1-301-816-8379