Potassium Nitrate

Potassium Nitrate BP: KNO3 -- 101.1 -- 7757-79-1

DEFINITION: Potassium nitrate contains not less than 99.0 per cent and not more than the equivalent of 101.0 per cent of KNO3, calculated with reference to the dried substance.

IDENTIFICATION

It gives the reaction of nitrates.Solution S (see Tests) gives the reactions of potassium.

• TESTS Solution S: Dissolve 10.0 g in carbon dioxide-free water prepared from distilled water and dilute to 100 ml with the same solvent.
• Appearance of solution: Solution S is clear and colourless.
• Acidity or alkalinity: To 10 ml of solution S add 0.05 ml of bromothymol blue solution. Not more than 0.5 ml of 0.01 M hydrochloric acid or 0.01 M sodium hydroxide is required to change the colour of the indicator.
• Reducible substances: To 10 ml of solution S, add 0.5 ml of dilute sulphuric acid and 2 ml of zinc iodide  and starch solution. The solution does not become blue within 2 min.
• Chlorides: If intended for ophthalmic use, it complies with the test for chlorides. Dissolve 2.5 g in water and dilute to 15 ml with the same solvent. The solution complies with the limit test for chlorides (20 ppm).
• Sulphates: Dilute 10 ml of solution S to 15 ml with distilled water. The solution complies with the limit test for sulphates (150 ppm).
• Ammonium: 1 ml of solution S complies with the limit test (A) for ammonium (100 ppm). If intended for ophthalmic use, not more than 50 ppm of ammonium.
• Calcium: Dilute 10 ml of solution S to 15 ml with distilled water. The solution complies with the limit test for calcium (100 ppm). If intended for ophthalmic use, not more than 50 ppm of calcium.
• Iron: Dilute 5 ml of solution S to 10 ml with water. The solution complies with the limit test for iron (20 ppm). If intended for ophthalmic use, not more than 10 ppm of iron.
• Sodium: Not more than 0.1 per cent of Na, determined by atomic emission spectrometry.
• Heavy metals: 12 ml of solution S complies with limit test A for heavy metals (10 ppm).
• Loss on drying: Not more than 0.5 per cent determined on 1.000 g by drying in an oven at 100C to 105C.