Packaging and storage—
Preserve in tight containers.
Identification—
It responds to the tests for
Potassium 
191
and for
Nitrate 191.
Chloride 221—
An accurately measured portion of Solution, equivalent to 500 mg of potassium nitrate, shows no more chloride than corresponds to 0.21 mL of 0.020 N hydrochloric acid (0.03%, based on the potassium nitrate content of the Solution).
Sulfate 221—
Dilute an accurately measured portion of Solution, equivalent to 100 mg of potassium nitrate, with water to obtain 10 mL of solution, add 15 mL of 6 N hydrochloric acid, and evaporate to dryness on a steam bath. To the residue so obtained add 7 mL of 6 N hydrochloric acid, and evaporate to dryness on a steam bath. Dissolve the residue so obtained in about 35 mL of 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 0.10 mL of 0.020 N sulfuric acid (0.1%, based on the potassium nitrate content of the Solution).
Arsenic, Method I 211:
3 ppm, based on the potassium nitrate content of the Solution, an accurately measured portion of Solution, equivalent to 1.0 g of potassium nitrate, being tested.
Lead—
Dilute an accurately measured portion of Solution, equivalent to 500 mg of potassium nitrate, with water to obtain 20 mL of test solution. This test solution contains not more than 5 µg 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 251.
Iron 241:
not more than 0.001%, based on the potassium nitrate content of the Solution, an accurately measured portion of Solution, equivalent to 1.0 g of potassium nitrate, being tested.
Limit of sodium—
Stock test solution—
Transfer an accurately measured portion of Solution, equivalent to 1.0 g of potassium nitrate, to a 500-mL volumetric 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.]
Procedure—
Proceed as directed in the
Limit of sodium test under
Potassium Nitrate. Calculate the percentage of sodium in the portion of Solution taken by multiplying
C by 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 nitrite test under
Potassium Nitrate.
Test solution—
Transfer an accurately measured portion of the Solution, equivalent to 4.0 g of potassium nitrate, to a 50-mL beaker, add sufficient water to obtain 20 mL of solution, and mix.
Procedure—
Proceed as directed in the
Limit of nitrite test under
Potassium Nitrate. The absorbance of the solution from the
Test solution does not exceed that of the solution from the
Standard solution containing 20 µg of nitrite (5 µg 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 20 cm.
Procedure—
Transfer an accurately measured portion of Solution, equivalent to about 400 mg of potassium nitrate, to a beaker and add sufficient water to obtain 100 mL of solution. Proceed as directed in the
Assay under
Potassium Nitrate beginning with “Pass this solution through . . . .” Each mL of 0.1 N sodium hydroxide is equivalent to 10.11 mg of KNO
3.
