3Zn(OH)2·2ZnCO3 549.01

Basic zinc carbonate.
Zinc subcarbonate [3486-35-9].

Packaging and storage— Preserve in tight containers.

Identification— A solution of it in a slight excess of hydrochloric acid responds to the tests for Zinc 191.

Insoluble matter— Dissolve a 10-g portion in a mixture of 100 mL of water and 7 mL of sulfuric acid, and heat on a steam bath for 1 hour. Filter the solution through a tared sintered-glass crucible, wash with hot water, dry the crucible at 105, cool, and weigh: the residue weighs not more than 20 mg (0.02%).

Chloride 221— A 1.0-g portion dissolved in a mixture of 20 mL of water and 3 mL of nitric acid shows no more chloride than corresponds to 0.03 mL of 0.02 N hydrochloric acid (0.002%).

Sulfate— Dissolve a 10.0-g portion in a mixture of 75 mL of water and 10 mL of hydrochloric acid, and filter. Neutralize the filtrate with ammonium hydroxide, dilute with water to 100 mL, and mix. To 10.0 mL of this solution add 1 mL of 0.6 N hydrochloric acid and 1 mL of barium chloride TS, mix, and allow to stand for 10 minutes. This test solution shows no more turbidity, if any, than that produced in a solution containing 0.10 mL of 0.02 N sulfuric acid and the same quantities of reagents used to prepare the test solution (0.01%).

Iron 241— Dissolve a 1.0-g portion in 20 mL of water and 3 mL of hydrochloric acid: the limit is 0.002%.

Lead— Transfer a 10.0-g portion to a 100-mL volumetric flask, add 20 mL of nitric acid and 10 mL of water, swirl to dissolve, dilute with water to volume, and mix. Add 10.0 mL of this solution to each of three 25-mL volumetric flasks. To respective volumetric flasks add 0, 5.0, and 10.0 mL of Standard Lead Solution, prepared as directed in the test for Heavy metals 231, dilute with water to volume, and mix. These solutions contain 0 (Test preparation), 0.002, and 0.004 mg of added lead per mL, respectively. Concomitantly determine the absorbances of these three solutions at the lead emission line at 217.0 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 in 25 solution of nitric acid in water to set the instrument to zero. Plot the absorbances of the three solutions versus their contents of added lead, in mg per mL, as furnished by the Standard Lead Solution, draw the straight line best fitting the three points, and extrapolate the line until it intercepts the concentration axis. From the intercept determine the amount, in mg, in each mL of the Test preparation. Calculate the quantity, in ppm, of lead in the specimen by multiplying this value by 25,000: the limit is 5 ppm.

Substances not precipitated by ammonium sulfide— Dissolve a 1.0-g portion in 10 mL of water and 2 mL of sulfuric acid, dilute with water to 80 mL, add 10 mL of ammonium hydroxide, and pass hydrogen sulfide through the solution for about 30 minutes. Dilute with water to 100 mL, and allow the precipitate to settle. Decant the supernatant through a filter, and transfer 50 mL of the clear filtrate to a tared dish, evaporate to dryness, ignite, gently at first and finally at 800 ± 25, cool, and weigh: the weight of the residue does not exceed 2 mg (0.4%).

Assay— Transfer about 2.0 g of Zinc Carbonate, accurately weighed, to a 125-mL conical flask, add 50.0 mL of 1 N sulfuric acid VS, and swirl to dissolve. Add 3 drops of methyl orange TS, and titrate with 1 N sodium hydroxide VS to a yellow endpoint. Each mL of 1 N sulfuric acid consumed is equivalent to 40.69 mg of ZnO.

Topic/Question	Contact	Expert Committee
Monograph	Feiwen Mao, M.S. Scientist 1-301-816-8320	(MDOOD05) Monograph Development-Ophthalmics Oncologics and Dermatologicals

USP32–NF27 Page 3894