0.9(0.02C)

Standard solutions— Transfer 2.542 g of sodium chloride, previously dried at 105 for 2 hours, to a 1000-mL volumetric flask. Dissolve in and dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a second 100-mL volumetric flask, dilute with water to volume, and mix. To three separate 100-mL volumetric flasks, transfer 1.0-, 3.0-, and 5.0-mL portions of this stock standard solution, dilute with water to volume, and mix. These solutions contain 1.0 µg, 3.0 µg, and 5.0 µg of sodium per mL, respectively.

Test solution— Use the stock solution used to prepare the Assay preparation in the Assay. Pass, if necessary, through a filter having a 0.5-µm or finer porosity to obtain a clear solution. Transfer 10.0 mL of the clear solution to a 25-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Standard solutions and the Test solution at the sodium emission line at 589.6 nm with an atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a sodium hollow-cathode lamp and an air–acetylene flame, using water as the blank. Plot the absorbances of the Standard solutions versus their contents of sodium, in µg per mL, by drawing a straight line best fitting the three plotted points. From the graph so obtained determine the quantity, C, in µg, of sodium in each mL of the Test solution. Calculate the quantity of sodium, in mg, per Lozenge by the formula: in which N is the number of Lozenges taken to prepare the Assay preparation. It contains not more than 115.0% of the declared amount.

Lanthanum chloride solution— Transfer 10 g of potassium chloride and 20 g of lanthanum chloride to a 2000-mL volumetric flask. Add about 1000 mL of water and 40 mL of hydrochloric acid, mix, and allow to cool. Dilute with water to volume, and mix.

1 N Hydrochloric acid— Transfer 83 mL of hydrochloric acid to a 1000-mL volumetric flask containing about 500 mL of water, mix, and allow to cool. Dilute with water to volume, and mix.

Standard preparations— Transfer about 250 mg of chelometric standard calcium carbonate, previously dried at 110 for 2 hours and then cooled in a desiccator and accurately weighed, to a 500-mL volumetric flask. Add about 100 mL of water and 12 mL of 1 N Hydrochloric acid, swirl to dissolve the calcium carbonate, and allow to cool. Dilute with water to volume, and mix. This stock solution contains about 500 µg of calcium carbonate per mL. To three separate 100-mL volumetric flasks add 2.0, 3.0, and 4.0 mL of this stock solution, dilute each with Lanthanum chloride solution to volume, and mix. These Standard preparations contain about 10, 15, and 20 µg of calcium carbonate per mL, respectively.

Assay preparation— Powder an accurately counted number of Lozenges, equivalent to about 3000 mg of calcium carbonate. Transfer the powder to a 1000-mL volumetric flask, add 100 mL of 1 N Hydrochloric acid and 300 mL of water, and sonicate to dissolve the powder. Dilute with water to volume, and mix. Transfer 5.0 mL of this solution to a 1000-mL volumetric flask, dilute with Lanthanum chloride solution to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparations and the Assay preparation at the calcium emission line at 422.7 nm with an atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a calcium hollow-cathode lamp and a nitrous oxide–acetylene flame, using Lanthanum chloride solution as the blank. Plot the absorbances of the Standard preparations versus their concentrations of calcium carbonate, in µg per mL, by drawing a straight line best fitting the three plotted points. From the graph so obtained, determine the concentration, C, in µg per mL, of calcium carbonate in the Assay preparation. Calculate the quantity, in mg, of calcium carbonate (CaCO3) per Lozenge by the formula: in which N is the number of Lozenges taken to prepare the Assay preparation.