Bismuth Subcarbonate
» Bismuth Subcarbonate contains not less than 97.6 percent and not more than 100.7 percent of (BiO)2CO3, calculated on the dried basis.
Packaging and storage— Preserve in well-closed containers, protected from light.
Identification— It responds to the tests for Bismuth 191 and for Carbonate 191.
Loss on drying 731 Dry it at 105 to constant weight: it loses not more than 1.0% of its weight.
Chloride 221 Mix 5.0 g of it with 10 mL of water, add 20 mL of nitric acid, warm to achieve dissolution, allow to cool, and dilute with water to obtain 100 mL of solution. To 6.6 mL of this stock solution add 4 mL of nitric acid, and dilute with water to obtain 50 mL of solution. A 15.0-mL portion of this test solution shows no more chloride than corresponds to 70 µL of 0.020 N hydrochloric acid (0.05%).
Limit of alkalies and alkaline earths— Boil 1.0 g of it with 20 mL of a mixture of acetic acid and water (1:1). After 2 minutes, cool and filter. Collect the filtrate, wash the residue with 20 mL of water, and add the washing to the filtrate. To this solution add 2 mL of 2 N hydrochloric acid and 20 mL of water. Heat to boiling and precipitate the bismuth by adding hydrogen sulfide. Cool the mixture, and filter. Collect the filtrate, wash the residue with water, and add the washing to the filtrate. Evaporate this solution to dryness on a water bath. To the residue add 0.5 mL of sulfuric acid, dry slowly, and cool: the weight of the residue does not exceed 10 mg (1.0%).
Limit of nitrate—
Indigo carmine titrant— Dissolve 4 g of indigo carmine in 900 mL of water, add 2 mL of sulfuric acid, and dilute with water to 1000 mL.
Standard solution— Prepare a solution of potassium nitrate in water containing 0.0815 mg per mL (equivalent to 0.05 mg of nitrate per mL). Add 20.0 mL of this solution to a 125-mL conical flask (Standard solution).
Test preparation— To 250 mg of Bismuth Subcarbonate in a 125-mL conical flask add 20 mL of water, and swirl to suspend.
Procedure— To the Standard solution and the Test preparation add 0.05 mL of Indigo carmine titrant. Carefully add 30 mL of sulfuric acid, and immediately titrate with Indigo carmine titrant to a stable blue endpoint. The volume of Indigo carmine titrant consumed by the Test preparation does not exceed that consumed by the Standard solution (0.4%).
Limit of silver— To 2.0 g of Bismuth Subcarbonate add 1 mL of water and 4 mL of nitric acid. Heat gently to achieve dissolution, add water to obtain 11 mL of solution, and cool. Add 2 mL of 1 N hydrochloric acid, and allow to stand in a dark place for 5 minutes. No more turbidity is produced than corresponds to that produced with 10 mL of a solution containing 7.87 µg of silver nitrate per mL concomitantly treated with 1 mL of nitric acid and 2 mL of 1 N hydrochloric acid (0.0025%).
Arsenic, Method I 211 Prepare the Test Preparation by dissolving 600 mg of it in 35 mL of 3 N hydrochloric acid. The limit is 5 µg per g.
Limit of copper—
Standard solution— To a 100-mL volumetric flask add 1.34 g of cupric chloride, 10 g of ammonium chloride, and 3 mL of sodium metabisulfite solution (275 mg per mL). Dilute with water to volume, and mix. This stock solution contains the equivalent of 5 mg of copper per mL. Dilute an accurately measured volume of this solution quantitatively and stepwise with 2 N nitric acid to obtain a solution containing the equivalent of 10 µg of copper per mL. Mix 0.25 mL of this solution and 9.75 mL of water (Standard solution).
Test solution— To 5 mL of the stock solution retained from the test for Chloride add 2 mL of 6 N ammonium hydroxide, dilute with water to 50 mL, mix, and filter. Use the filtrate as the Test solution.
Procedure— To 10 mL of the Standard solution and the Test solution add 1 mL of a solution of sodium diethyldithiocarbamate (1 in 1000): no more color is obtained from the Test solution than is obtained from the Standard solution (0.005%).
Limit of lead—
Diluent— Use 6 N nitric acid that is lead-free.
Standard solutions— Prepare a solution of lead nitrate in Diluent containing 0.1598 mg per mL. This solution contains 100 µg of lead per mL. Dilute an accurately measured volume of this solution, quantitatively and stepwise, with Diluent to obtain Standard solutions containing 1.0, 2.0, and 3.0 µg of lead per mL.
Test solution— Dissolve 12.5 g of Bismuth Subcarbonate in 75 mL of Diluent. Heat to boiling for 1 minute, cool, and dilute with water to 100 mL.
Procedure— Concomitantly determine the absorbances of the Standard solutions and the Test solution at the lead emission line of 283.3 nm with an atomic absorption spectrophotometer (see Spectrophotometry and Light-scattering 851) equipped with a lead hollow-cathode lamp and an air–acetylene flame, using a 1:5 dilution of the Diluent as the blank. Plot the absorbances of the Standard solutions versus concentration, in µg per mL, of lead, and draw the straight line best fitting the three plotted points. From the graph so obtained, determine the concentration, C, in µg per mL, of lead in the Test solution. Calculate the percentage of lead (Pb) in the portion of Bismuth Subcarbonate taken by the formula:
C / 12,500.
The limit is 0.002%.
Assay— Dissolve about 500 mg of Bismuth Subcarbonate, accurately weighed, in 3 mL of nitric acid. Dilute with water to 250 mL, add 0.3 mL of xylenol orange TS, and titrate with 0.05 M edetate disodium VS to a yellow endpoint. Each mL of 0.05 M edetate disodium is equivalent to 12.75 mg of (BiO)2CO3.
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