Medium: water; 900 mL.

Apparatus 1: 100 rpm.

Time: 30 minutes.

Procedure— Determine the amount of Li2CO3 dissolved in filtered portions of the solution under test with a suitable flame photometer, as directed in the Assay.

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

(Official January 1, 2007)

Standard preparation— Transfer to a 100-mL volumetric flask about 30 mg of USP Lithium Carbonate RS, accurately weighed. Add about 20 mL of water and 0.5 mL of hydrochloric acid, shake until dissolved, dilute with water to volume, and mix. Pipet 20 mL of the resulting solution into a 1000-mL volumetric flask, add about 800 mL of water and 20 mL of a suitable surfactant solution, appropriately diluted, dilute with water to volume, and mix.

Assay preparation— Empty as completely as possible the contents of not less than 20 Capsules. 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 sample 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— Employ a suitable flame photometer, and adjust the instrument with the surfactant solution. Aspirate into the photometer the Standard preparation and the Assay preparation, and measure the emission at about 671 nm. Calculate the quantity, in mg, of Li2CO3 in the portion of Capsules 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.