A: Infrared Absorption 197K.

B: Add a few drops of sodium nitroferricyanide TS to 2 mL of a solution of Erythorbic Acid and water (1:50), and add 1 mL of 0.1 N sodium hydroxide. A transient blue color immediately appears.

C: Dissolve about 15 mg of Erythorbic Acid in 15 mL of trichloroacetic acid solution (1:20), add about 200 mg of activated charcoal, and shake the mixture vigorously for 1 minute. Pass through a small fluted filter, refiltering if necessary to obtain a clear filtrate. Add 1 drop of pyrrole to 5 mL of the clear filtrate, agitate the mixture until the pyrrole is dissolved, and heat in a water bath at 50. A blue color appears.

Test solution— Transfer about 2.5 g of Erythorbic Acid, accurately weighed, into a 25-mL volumetric flask, dissolve in about 20 mL of water, and dilute with water to volume.

Standard stock solution— Dissolve about 160 mg of lead nitrate, accurately weighed, in 100 mL of water containing 1 mL of nitric acid. Dilute with water to 1000 mL, and mix.

Standard solutions— [note—Prepare these solutions on the day of use.] Transfer 10.0 mL of Standard stock solution to a 100-mL volumetric flask, dilute with water to volume, and mix. Each mL of this solution contains the equivalent of about 10 µg of lead. Dilute accurately measured volumes of the diluted standard solution with water to obtain solutions having known concentrations of about 1 µg, 2 µg, and 5 µg of lead per mL.

Test solution— Transfer about 10 g of Erythorbic Acid, accurately weighed, to an evaporating dish. Add 5 mL of a 25% sulfuric acid solution, and distribute the sulfuric acid uniformly through the sample. Within a hood, place the dish on a steam bath to evaporate most of the water. Place the dish on a burner, and slowly pre-ash the sample by expelling most of the sulfuric acid. Place the dish in a muffle furnace at 525, and ash the sample until the residue appears free from carbon. Prepare a blank by ashing 5 mL of a 25% sulfuric acid solution. Cool, and cautiously wash down the inside of each evaporation dish with water. Treat both the sample and the blank as follows. Add 5 mL of 1 N hydrochloric acid. Place each dish on a steam bath, and evaporate to dryness. To each dish add 1.0 mL of 3 N hydrochloric acid and approximately 5 mL of water, and heat briefly on a steam bath to dissolve any residue. Transfer each solution quantitatively to a 10-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Using a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a lead electrodeless discharge lamp, an air–acetylene flame, and a suitable burner head, perform a blank determination with water, following the manufacturer's operating instructions. Concomitantly determine the absorbances of the blank, the Standard solutions, and the Test solution at the lead emission line of 283.3 nm, using a slit width of 0.7 nm. Determine the corrected absorbance values by subtracting the absorbance of the blank from the absorbance of each of the Standard solutions and from the absorbance of the Test solution. Prepare a standard curve by plotting the corrected absorbance values of the Standard solutions versus their corresponding concentration, in µg per mL. From the calibration curve, determine the lead concentration in the Test solution. Calculate the lead content, in µg per g, in the portion of Erythorbic Acid taken by the formula: in which C is the concentration, in µg per mL, of lead from the standard curve; and W is the weight, in g, of Erythorbic Acid taken: not more than 10 µg per g is found.