A: Infrared Absorption á197Kñ.

B: Ultraviolet Absorption á197Uñ—

Mobile phase and Chromatographic system—Proceed as directed in the Assay.To evaluate the system suitability requirements,use the Standard preparationas prepared in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Methsuximide RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 6.0µg per mL.

Test solution— Transfer about 300mg of Methsuximide,accurately weighed,to a 50-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure all of the peak responses.Calculate the percentage of each impurity in the portion of Methsuximide taken by the formula: in which CSis the concentration,in µg per mL,of USP Methsuximide RSin the Standard solution;CUis the concentration,in mg per mL,of Methsuximide in the Test solution;riis the peak response for each impurity obtained from the Test solution;and rSis the peak response for methsuximide obtained from the Standard solution:not more than 0.1%of any individual impurity is found;and not more than 2.0%of total impurities is found.

Solvent— Use dimethyl sulfoxide.

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (11:9).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Methsuximide RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 0.6mg per mL.

Assay preparation— Transfer about 120mg of Methsuximide,accurately weighed,to a 200-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.

Chromatographic system— 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 for Procedure:the column efficiency is not less than 5800theoretical plates;the tailing factor is not more than 1.3;and the relative standard deviation for replicate injections is not more than 0.6%.

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 C12H13NO2in the portion of Methsuximide taken by the formula: in which CSis the concentration,in mg per mL,of USP Methsuximide RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.