A: Mix a portion of the contents of Capsules,equivalent to about 200mg of methsuximide,with 25mLof water in a separator,extract with 50mLof ether,and discard the aqueous layer.Wash the ether extract with 25mLof water,and discard the water.Filter the extract,evaporate with the aid of a current of warm air to dryness,and dry the methsuximide over phosphorus pentoxide for 16hours:the residue so obtained responds to Identificationtest Aunder Methsuximide.

B: The retention time exhibited by methsuximide in the chromatogram of the Assay preparationcorresponds to that of methsuximide in the chromatogram of the Standard preparationas obtained in the Assay.

Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 120minutes.

Procedure— Determine the amount of C12H13NO2dissolved,employing the procedure set forth in the Assay,making any necessary modifications.

Tolerances— Not less than 75%(Q)of the labeled amount of C12H13NO2is dissolved in 120minutes.

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (55:45).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Methsuximide RSin Mobile phaseto obtain a solution having a known concentration of about 0.6mg per mL.

Assay preparation— Place 10Capsules in a 500-mLvolumetric flask,and add 280mLof water.Sonicate in a water bath at 40to 50,with occasional shaking,until the Capsules have broken,and cool to room temperature.Dilute with acetonitrile to volume,mix,and filter.Transfer an accurately measured volume of this specimen solution,equivalent to about 30mg of methsuximide,to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the column efficiency determined from the analyte peak is not less than 2100theoretical plates,and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of methsuximide (C12H13NO2)per Capsule taken by the formula: in which Cis the concentration,in mg per mL,of USP Methsuximide RSin the Standard preparation;Vis the volume,in mL,of specimen solution taken for the Assay preparation;and rUand rSare the methsuximide peak responses obtained from the Assay preparationand the Standard preparation,respectively.