3Zn(OH)2·2ZnCO3 549.01

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

Packaging and storage— Preserve in tight containers.

Identification— Asolution of it in a slight excess of hydrochloric acid responds to the tests for Zinc á191ñ.

Insoluble matter— Dissolve a 10-g portion in a mixture of 100mLof water and 7mLof sulfuric acid,and heat on a steam bath for 1hour.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 20mg (0.02%).

Chloride á221ñ— A1.0-g portion dissolved in a mixture of 20mLof water and 3mLof nitric acid shows no more chloride than corresponds to 0.03mLof 0.02Nhydrochloric acid (0.002%).

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

Iron á241ñ— Dissolve a 1.0-g portion in 20mLof water and 3mLof hydrochloric acid:the limit is 0.002%.

Lead— Transfer a 10.0-g portion to a 100-mLvolumetric flask,add 20mLof nitric acid and 10mLof water,swirl to dissolve,dilute with water to volume,and mix.Add 10.0mLof this solution to each of three 25-mLvolumetric flasks.To respective volumetric flasks add 0,5.0,and 10.0mLof Standard Lead Solution,prepared as directed in the test for Heavy metals á231ñ,dilute with water to volume,and mix.These solutions contain 0(Test preparation),0.002,and 0.004mg of added lead per mL,respectively.Concomitantly determine the absorbances of these three solutions at the lead emission line at 217.0nm,with an atomic absorption spectrophotometer (see Spectrophotometry and Light-scattering á851ñ)equipped with a lead hollow-cathode lamp and an air–acetylene flame,using a 1in 25solution 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 mLof the Test preparation.Calculate the quantity,in ppm,of lead in the specimen by multiplying this value by 25,000:the limit is 5ppm.

Substances not precipitated by ammonium sulfide— Dissolve a 1.0-g portion in 10mLof water and 2mLof sulfuric acid,dilute with water to 80mL,add 10mLof ammonium hydroxide,and pass hydrogen sulfide through the solution for about 30minutes.Dilute with water to 100mL,and allow the precipitate to settle.Decant the supernatant through a filter,and transfer 50mLof 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 2mg (0.4%).

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

Expert Committee:(PA6)Pharmaceutical Analysis 6

USP28–NF23Page 2052

Phone Number:1-301-816-8389