Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 60minutes.

Procedure— [NOTE—Perform baseline corrections,if necessary,in determining the absorbance by extrapolating the baseline through the absorbance minima at about 300and 280nm and beyond 257nm.]Determine the amount of C12H14N2O2dissolved from UVabsorbances at the wavelength of maximum absorbance at about 257nm of filtered portions of the solution under test,suitably diluted with Dissolution Medium,if necessary,in comparison with a Standard solutionhaving a known concentration of USP Primidone RSin the same medium.

Tolerances— Not less than 75%(Q)of the labeled amount of C12H14N2O2is dissolved in 60minutes.

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

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

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

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector and a 4.0-mm ×120-cm column packed with 10%liquid phase G3on support S1AB.Helium is used as the carrier gas at a flow rate of about 40mLper minute.The detector and injector temperatures are maintained at about 310and 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 3µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 0.8for primidone and 1.0for androsterone.Calculate the quantity,in mg,of C12H14N2O2in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Primidone RSin the Standard preparation,and RUand RSare the relative response factors obtained from the Assay preparationand the Standard preparation,respectively.