Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 30 minutes.

Procedure— Determine the amount in solution by flame photometry, the test specimen being prepared by diluting the 900 mL of the solution under test to 1000 mL and a 20.0-mL filtered aliquot being transferred to a 1000-mL volumetric flask and treated with 500 mL of water, 1 drop of hydrochloric acid, and 20 mL of a suitable surfactant solution, appropriately diluted. Add water to volume, mix, and read on a suitable photometer together with the Standard preparation as directed in the Assay under Lithium Carbonate Capsules.

Tolerances— Not less than 80% (Q) of the labeled amount of Li2CO3 is dissolved in 30 minutes.

Standard preparation— Prepare as directed in the Assay under Lithium Carbonate Capsules.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Weigh accurately a portion of the powder, equivalent to about 600 mg of lithium carbonate, and transfer to a 1000-mL volumetric flask. Add 40 mL of water and 5 mL of hydrochloric acid, shake until the solid is well disintegrated, dilute with water to volume, and mix. Pipet 10 mL of the resulting solution into a 1000-mL volumetric flask, add about 800 mL of water and 20 mL of the surfactant solution, dilute with water to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay under Lithium Carbonate Capsules. Calculate the quantity, in mg, of Li2CO3 in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Lithium Carbonate RS in the Standard preparation, and A and S are the photometer readings of the Assay preparation and the Standard preparation, respectively.