美国药典重金属检查法.doc

231 HEAVY METALS This test is provided to demonstrate that the content of metallic impurities that are colored by sulfide ion, under the specified test conditions, does not exceed the Heavy metals limit specified in the individual monograph in percentage (by weight) of lead in the test substance, as determined by itant parison (see parison in the section Procedure under Spectrophotometry and Light-Scattering 851 ) with a control prepared from a Standard Lead Solution. [ NOTE — Substances that typically will respond to this test are lead, mercury, bismuth, arsenic, antimony, tin, cadmium, silver, copper, and molybdenum.] Determine the amount of heavy metals by Method I, unless otherwise specified in the individual monograph. Method I is used for substances that yield clear, colorless preparations under the specified test conditions. Method II is used for substances that do not yield clear, colorless preparations under the test conditions specified for Method I, or for substances that, by virtue of plex nature, interfere with the precipitation of metals by sulfide ion, or for fixed and volatile oils. Method III, a wet-digestion method, is used only in those cases where neither Method I nor Method II can be used. Special Reagents Lead Nitrate Stock Solution — Dissolve mg of lead nitrate in 100 mL of water to which has been added 1 mL of nitric acid, then dilute with water to