Potassium Nitrate Solution
»Potassium Nitrate Solution contains not less than 98.0percent and not more than 102.0percent of the labeled amount of KNO3.
Packaging and storage— Preserve in tight containers.
Identification— It responds to the tests for Potassium á191ñand for Nitrate á191ñ.
Chloride á221ñ— An accurately measured portion of Solution,equivalent to 500mg of potassium nitrate,shows no more chloride than corresponds to 0.21mLof 0.020Nhydrochloric acid (0.03%,based on the potassium nitrate content of the Solution).
Sulfate á221ñ— Dilute an accurately measured portion of Solution,equivalent to 100mg of potassium nitrate,with water to obtain 10mLof solution,add 15mLof 6Nhydrochloric acid,and evaporate to dryness on a steam bath.To the residue so obtained add 7mLof 6Nhydrochloric acid,and evaporate to dryness on a steam bath.Dissolve the residue so obtained in about 35mLof water and,if necessary,neutralize with hydrochloric acid using litmus paper indicator.Filter,if necessary,to obtain a clear test solution.This test solution shows no more sulfate than corresponds to 0.10mLof 0.020Nsulfuric acid (0.1%,based on the potassium nitrate content of the Solution).
Arsenic,Method Iá211ñ: 3ppm,based on the potassium nitrate content of the Solution,an accurately measured portion of Solution,equivalent to 1.0g of potassium nitrate,being tested.
Lead— Dilute an accurately measured portion of Solution,equivalent to 500mg of potassium nitrate,with water to obtain 20mLof test solution.This test solution contains not more than 5µg of lead (corresponding to not more than 0.001%of Pb,based on the potassium nitrate content of the Solution)when tested as directed under Lead á251ñ.
Heavy metals,Method Iá231ñ: 0.002%,based on the potassium nitrate content of the Solution.
Iron á241ñ: not more than 0.001%,based on the potassium nitrate content of the Solution,an accurately measured portion of Solution,equivalent to 1.0g of potassium nitrate,being tested.
Limit of sodium—
Stock test solution— Transfer an accurately measured portion of Solution,equivalent to 1.0g of potassium nitrate,to a 500-mLvolumetric flask,dilute with water to volume,and mix.[NOTE—The concentration of potassium nitrate in this solution may be modified by using a different quantity or by further dilution to bring the absorption response within the working range of the atomic absorption spectrophotometer.]
Stock standard solution— Proceed as directed in the Limit of sodiumtest under Potassium Nitrate.
Procedure— Proceed as directed in the Limit of sodiumtest under Potassium Nitrate.Calculate the percentage of sodium in the portion of Solution taken by multiplying Cby 0.25:the limit is 0.1%,based on the potassium nitrate content of the Solution.
Limit of nitrite—
Sulfanilic acid solution,N-(1-Naphthyl)ethylenediamine dihydrochloride solution,and Standard solutions— Proceed as directed in the Limit of nitritetest under Potassium Nitrate.
Test solution— Transfer an accurately measured portion of the Solution,equivalent to 4.0g of potassium nitrate,to a 50-mLbeaker,add sufficient water to obtain 20mLof solution,and mix.
Procedure— Proceed as directed in the Limit of nitritetest under Potassium Nitrate.The absorbance of the solution from the Test solutiondoes not exceed that of the solution from the Standard solutioncontaining 20µg of nitrite (5µg per g,based on the potassium nitrate content of the Solution).
Assay— [NOTE—Use water that is carbon dioxide-and ammonia-free.]
Cation-exchange column— Transfer strongly acidic styrene-divinylbenzene cation-exchange resin (16-to 50-mesh)to a 2-cm diameter chromatographic column to a depth of about 20cm.
Procedure— Transfer an accurately measured portion of Solution,equivalent to about 400mg of potassium nitrate,to a beaker and add sufficient water to obtain 100mLof solution.Proceed as directed in the Assayunder Potassium Nitratebeginning with “Pass this solution through ....”Each mLof 0.1Nsodium hydroxide is equivalent to 10.11mg of KNO3.
Auxiliary Information— Staff Liaison:Andrzej Wilk,Ph.D.,Senior Scientific Associate
Expert Committee:(PA5)Pharmaceutical Analysis 5
USP28–NF23Page 1597
Phone Number:1-301-816-8305