![]() ![]() This limit test is provided to demonstrate that the content of iron, in either the ferric or the ferrous form, does not exceed the limit for iron specified in the individual monograph. The determination is made by concomitant visual comparison with a control prepared from a standard iron solution.
Special Reagents— ![]() ![]() Standard Preparation— Into a 50-mL color-comparison tube pipet 1 mL of Standard Iron Solution (10 µg of Fe), dilute with water to 45 mL, add 2 mL of hydrochloric acid, and mix. Test Preparation— Into a 50-mL color comparison tube place the solution prepared for the test as directed in the individual monograph and if necessary dilute with water to 45 mL; or, dissolve in water, and dilute with water to 45 mL the quantity, in g, of the substance to be tested, as calculated by the formula: 1.0 / (1000L)
in which L is the Iron limit in percentage. Add 2 mL of hydrochloric acid, and mix.
Procedure— To each of the tubes containing the Standard Preparation and the Test Preparation add 50 mg of ammonium peroxydisulfate crystals and 3 mL of Ammonium Thiocyanate Solution, and mix: the color of the solution from the Test Preparation is not darker than that of the solution from the Standard Preparation. Auxiliary Information— Please check for your question in the FAQs before contacting USP.
USP32–NF27 Page 136
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