A: A solution (1 in 20) responds to the test for Copper 191.

B: It responds to Identification test B under Calcium Gluconate.

Standard preparation— Transfer 10.0 mL of Lead Nitrate Stock Solution, prepared as directed in the test for Heavy Metals 231, to a 100-mL volumetric flask, add 40 mL of water and 5 mL of nitric acid, dilute with water to volume, and mix. Transfer 0.40 mL of this solution to a second 100-mL volumetric flask, add 50 mL of water and 1 mL of nitric acid, dilute with water to volume, and mix. This solution contains 0.04 µg of lead per mL.

Test preparation— Transfer about 4 g of Copper Gluconate, accurately weighed, to a 100-mL volumetric flask. Add 50 mL of water and 5 mL of nitric acid, and sonicate to dissolve the specimen. Dilute with water to volume, and mix. Transfer 4.0 mL of this solution to a second 100-mL volumetric flask, add 50 mL of water and 1 mL of nitric acid, dilute with water to volume, and mix.

Blank— Transfer 1.2 mL of nitric acid to a 100-mL volumetric flask, dilute with water to volume, and mix.

Test solutions— Prepare mixtures of the Test preparation, the Standard preparation, and the Blank with the following proportional compositions, by volume: 10.0:0:10.0, 10.0:4.0:6.0, 10.0:7.0:3.0, and 10.0:10.0:0. These Test solutions contain, respectively, 0, 0.008, 0.014, and 0.020 µg per mL, of lead from the Standard preparation.

Procedure— Separately inject equal volumes (about 20 µL) of the Test solutions and the Blank into the graphite tube of a suitable graphite furnace atomic absorption spectrophotometer, temperature-programmed as follows to reach 2000 in about 2 minutes, using an argon gas flow of about 3 L per minute, except where indicated: 70 for 10 seconds, 90 for 60 seconds, 120 for 15 seconds, 250 for 5 seconds (no gas flow), 250 for 10 seconds, 250 for 2 seconds (no gas flow), and 2000 for 3.2 seconds. When the temperature reaches 2000, determine the absorbance at the lead emission line at 283.3 nm, corrected for background absorption. Correct the absorbance values obtained from the Test solutions by subtracting from each the absorbance value obtained from the Blank. Plot the corrected absorbances of the Test solutions versus their contents of lead, in µg per mL, as furnished by the Standard preparation, draw the straight line best fitting the four points, and extrapolate the line until it intercepts the concentration axis. From the intercept determine the concentration, C, in µg per mL, of lead in each mL of the test solution containing 0 µg of lead from the Test preparation. Calculate the percentage of lead in the specimen taken by the formula: in which W is the weight, in g, of Copper Gluconate taken to prepare the Test preparation: the limit is 0.0025%.