A: Asolution (1in 10)responds to the tests for Zinc á191ñ.

B: It responds to Identificationtest Bunder Calcium Gluconate.

Standard preparation— Transfer 137.2mg of cadmium nitrate to a 1000-mLvolumetric flask,dissolve in water,dilute with water to volume,and mix.Pipet 25mLof the resulting solution into a 100-mLvolumetric flask,add 1mLof hydrochloric acid,dilute with water to volume,and mix.Each mLof this Standard preparationcontains 12.5µg of Cd.

Test preparation— Transfer 10.0g of Zinc Gluconate to a 50-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.

Procedure— To three separate 25-mLvolumetric flasks add,respectively,0,2.0,and 4.0mLof the Standard preparation.To each flask add 5.0mLof the Test preparation,dilute with water to volume,and mix.These test solutions contain,respectively,0,1.0,and 2.0µg per mLof cadmium from the Standard preparation.Concomitantly determine the absorbances of the test solutions at the cadmium emission line at 228.8nm,with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-scattering á851ñ)equipped with a cadmium hollow-cathode lamp and an air–acetylene flame,using water as the blank.Plot the absorbances of the test solutions versus their contents of cadmium,in µg per mL,as furnished by the Standard preparation,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 µg,of cadmium in each mLof the test solution containing 0mLof the Standard preparation.Calculate the quantity,in ppm,of Cd in the specimen by multiplying this value by 25:the limit is 5ppm.

Ascorbic acid–sodium iodide solution— Dissolve 20g of ascorbic acid and 38.5g of sodium iodide in water in a 200-mLvolumetric flask,dilute with water to volume,and mix.

Trioctylphosphine oxide solution— [Caution—This solution causes irritation.Avoid contact with eyes,skin,and clothing.Take special precautions in disposing of unused portions of solutions to which this reagent is added. ]Dissolve 5.0g of trioctylphosphine oxide in 4-methyl-2-pentanone in a 100-mLvolumetric flask,dilute with the same solvent to volume,and mix.

Standard solutionand Blank— Transfer 5.0mLof Lead Nitrate Stock Solution,prepared as directed in the test for Heavy Metals á231ñ,to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 2.0mLof the resulting solution to a 50-mLvolumetric flask.To this volumetric flask and to a second,empty 50-mLvolumetric flask(Blank)add 10mLof 9Nhydrochloric acid and about 10mLof water.To each flask add 20mLof Ascorbic acid–sodium iodide solutionand 5.0mLof Trioctylphosphine oxide solution,shake for 30seconds,and allow to separate.Add water to bring the organic solvent layer into the neck of each flask,shake again,and allow to separate.The organic solvent layers are the Blankand the Standard solution,and they contain 0.0µg and 2.0µg of lead per mL,respectively.

Test solution— Add 1.0g of Zinc Gluconate,10mLof 9Nhydrochloric acid,about 10mLof water,20mLof Ascorbic acid–sodium iodide solution,and 5.0mLof Trioctylphosphine oxide solutionto a 50-mLvolumetric flask,shake for 30seconds,and allow to separate.Add water to bring the organic solvent layer into the neck of the flask,shake again,and allow to separate.The organic solvent layer is the Test solution.

Procedure— Concomitantly determine the absorbances of the Blank,Standard solution,and Test solutionat the lead emission line at 283.3nm,with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with a lead hollow-cathode lamp and an air–acetylene flame,using the Blankto set the instrument to zero.In a suitable analysis,the absorbance of the Standard solutionand the absorbance of the Blank are significantly different:the absorbance of the Test solutiondoes not exceed that of the Standard solution(0.001%).