(Official January 1, 2007)

Sodium chloride solution— Dissolve 2.7 g of sodium chloride in water, dilute with water to 2000 mL, and mix.

Copper stock solution— Transfer 1.000 g of copper to a 1000-mL volumetric flask, dissolve in 20 mL of nitric acid, dilute with 0.2 N nitric acid to volume, and mix. This solution contains 1000 µg of copper per mL. Store in a polyethylene bottle.

Standard preparations— Pipet 15 mL of Copper stock solution into a 250-mL volumetric flask, dilute with water to volume, and mix. Transfer 4.0, 5.0, and 6.0 mL of this solution to separate 100-mL volumetric flasks containing 10 mL of Sodium chloride solution, dilute the contents of each flask with water to volume, and mix. These Standard preparations contain, respectively, 2.4, 3.0, and 3.6 µg of copper per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 2 mg of copper, to a 100-mL volumetric flask, dilute with water to volume, and mix. Pipet 15 mL of this solution into a 100-mL volumetric flask. From the labeled amount of sodium chloride, if any, in the Injection, calculate the amount, in mg, of sodium chloride in the initial dilution, and add sufficient Sodium chloride solution to bring the total sodium content of this flask to 13.5 mg. Dilute with water to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparations and the Assay preparation at the copper emission line of 324.8 nm, with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-scattering 851) equipped with a copper hollow-cathode lamp and an air–acetylene flame using a 1 in 10 dilution of Sodium chloride solution as the blank. Plot the absorbances of the Standard preparations versus concentration, in µg per mL, of copper, and draw the straight line best fitting the three plotted points. From the graph so obtained, determine the concentration, in µg per mL, of copper in the Assay preparation. Calculate the quantity, in mg, of copper in each mL of the Injection taken by the formula: in which C is the concentration, in µg per mL, of copper in the Assay preparation; and V is the volume, in mL, of Injection taken.