A: Triturate a quantity of finely powdered Tablets, equivalent to about 60 mg of phenobarbital, with 50 mL of chloroform, and filter. Evaporate the clear filtrate to dryness, and dry at 105 for 2 hours: the residue so obtained responds to Identification test A under Phenobarbital.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that of the Standard preparation, both relative to the internal standard, as obtained in the Assay.

Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C12H12N2O3 dissolved from UV absorbances at the wavelength of maximum absorbance at about 240 nm on filtered portions of the solution under test, suitably diluted with pH 9.6 alkaline borate buffer (see Buffer Solutions in the section Reagents, Indicators, and Solutions), in comparison with a Standard solution having a known concentration of USP Phenobarbital RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C12H12N2O3 is dissolved in 45 minutes.

pH 4.5 Buffer solution, Mobile phase, Internal standard solution, Standard preparation, and Chromatographic system— Prepare as directed in the Assay under Phenobarbital.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Weigh accurately a portion of the powder, equivalent to about 20 mg of phenobarbital, add 15.0 mL of Internal standard solution, mix, and sonicate for 15 minutes. Filter through a membrane filter having a 0.5-µm or finer porosity before use.

Procedure— Proceed as directed for Procedure in the Assay under Phenobarbital. Calculate the quantity, in mg, of C12H12N2O3 in the portion of Tablets taken by the formula: in which the terms are as defined therein.