K2HPO4 174.18

Phosphoric acid,dipotassium salt.
Dipotassium hydrogen phosphate [7758-11-4].

Packaging and storage— Preserve in well-closed containers.

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

pHá791ñ: between 8.5and 9.6,in a solution (1in 20).

Loss on drying á731ñ— Dry it at 105to constant weight: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 weight of the residue so obtained does not exceed 20mg (0.2%).

Carbonate— To 1g add 3mLof water and 2mLof 3Nhydrochloric acid:not more than a few bubbles are evolved.

Chloride á221ñ— A1.0-g portion shows no more chloride than corresponds to 0.40mLof 0.020Nhydrochloric acid (0.03%).

Sulfate á221ñ— A0.20-g portion shows no more sulfate than corresponds to 0.20mLof 0.020Nsulfuric acid (0.1%).

Arsenic,Method Iá211ñ: 3ppm.

Iron— Dissolve 0.33g in 10mLof water,add 6mLof hydroxylamine hydrochloride solution (1in 10)and 4mLof orthophenanthroline solution prepared by dissolving 1g of orthophenanthroline in 1000mLof water containing 1mLof 3Nhydrochloric acid,and dilute with water to 25mL:any red color produced within 1hour is not darker than that of a control prepared from 1mLof Standard Iron Solution(see Iron á241ñ):the limit is 0.003%.

Sodium á191ñ— Asolution (1in 10)tested on a platinum wire imparts no pronounced yellow color to a nonluminous flame.

Heavy metals,Method Iá231ñ: Dissolve a portion equivalent to 4.2g of K2HPO4in enough water to make 50mLof stock solution.Transfer 12mLof this stock solution to a 50-mLcolor-comparison tube (Test Preparation).Transfer 11mLof the stock solution to a second color-comparison tube containing 1.0mLof Standard Lead Solution(Monitor Preparation).Transfer 1.0mLof Standard Lead Solutionand 11mLof water to a third color-comparison tube (Standard Preparation).Proceed as directed for Procedure,omitting the dilution to 50mL:the limit is 0.001%.

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

Limit of monobasic or tribasic salt— Dissolve 3g in 30mLof water,cool to 20,and add 3drops of thymol blue TS:a blue color is produced,which is changed to yellow (with a greenish tinge)by the addition of not more than 0.4mLof 1Nhydrochloric acid.

Assay— Transfer 40.0mLof 1Nhydrochloric acid to a 250-mLbeaker,add 50mLof water,and titrate potentiometrically with 1Nsodium hydroxide VSto the endpoint.Record the volume of 1Nsodium hydroxide VSconsumed as the blank.Transfer about 5.2g of Dibasic Potassium Phosphate,accurately weighed,to a 250-mLbeaker,add 50mLof water and 40.0mLof 1Nhydrochloric acid VS,stir until dissolved,and proceed as directed in the Assayunder Dibasic Sodium Phosphate,beginning with “Titrate the excess acid.”Where Ais equal to or less than B,each mLof the volume Aof 1Nsodium hydroxide is equivalent to 174.2mg of K2HPO4.Where Ais greater than B,each mLof the volume 2B-Aof 1Nsodium hydroxide is equivalent to 174.2mg of K2HPO4.

Expert Committee:(PA4)Pharmaceutical Analysis 4

USP28–NF23Page 1598

Phone Number:1-301-816-8251