Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 60 minutes.

Procedure— [note—Perform baseline corrections, if necessary, in determining the absorbance by extrapolating the baseline through the absorbance minima at about 300 and 280 nm and beyond 257 nm.] Determine the amount of C12H14N2O2 dissolved from UV absorbances at the wavelength of maximum absorbance at about 257 nm of filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Primidone RS in the same medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C12H14N2O2 is dissolved in 60 minutes.

Internal standard solution— Dissolve a suitable quantity of androsterone in alcohol to obtain a solution having a final concentration of about 10 mg per mL.

Standard preparation— Transfer about 100 mg of USP Primidone RS, accurately weighed, to a 100-mL volumetric flask, add 65 mL of alcohol, and boil for 1 hour. Allow to cool to ambient temperature, add 10.0 mL of Internal standard solution, dilute with alcohol to volume, mix, and filter.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 50 mg of primidone, to a 50-mL volumetric flask, add 35 mL of alcohol, and boil for 1 hour. Allow to cool to ambient temperature, add 5.0 mL of Internal standard solution, dilute with alcohol to volume, mix, and filter.

Chromatographic system (see Chromatography 621)—The gas chromatograph is equipped with a flame-ionization detector and a 4.0-mm × 120-cm column packed with 10% liquid phase G3 on support S1AB. Helium is used as the carrier gas at a flow rate of about 40 mL per minute. The detector and injector temperatures are maintained at about 310 and the column temperature is maintained at about 260. Chromatograph three replicate injections of the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation is not more than 2.0%, and the resolution factor between primidone and androsterone is not less than 1.5.

Procedure— Separately inject equal volumes (about 3 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.8 for primidone and 1.0 for androsterone. Calculate the quantity, in mg, of C12H14N2O2 in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Primidone RS in the Standard preparation, and RU and RS are the relative response factors obtained from the Assay preparation and the Standard preparation, respectively.