FOR ORAL SUSPENSION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.

FOR ORAL SUSPENSION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.

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— Transfer an accurately weighed quantity of well-mixed Oral Suspension,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 injection port 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 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 primidone (C12H14N2O2)in each mLof the Oral Suspension taken by the formula: in which Dis the density,in g per mL,of the Oral Suspension;WSis the weight,in mg,of the Standard used;WUis the weight,in mg,of Oral Suspension taken;and RUand RSare the relative response factors obtained from the Assay preparationand the Standard preparation,respectively.