Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 2: 100rpm.

Time: 60minutes.

Standard solution— Transfer about 100mg of USP Ethotoin RS,accurately weighed,to a 25-mLvolumetric flask.Dissolve in methanol,dilute with methanol to volume,and mix.Transfer 4.0mLof this solution to a 50-mLvolumetric flask,add Dissolution Mediumto volume,and mix.

Procedure— Determine the amount of C11H12N2O2dissolved from UVabsorbances at the wavelength of maximum absorbance at about 257nm on filtered portions of the solution under test,suitably diluted with Dissolution Medium,if necessary,in comparison with the Standard solution.

Tolerances— Not less than 80%(Q)of the labeled amount of C11H12N2O2is dissolved in 60minutes.

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (3:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution of ethylparaben in Mobile phasehaving a concentration of 0.02mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Ethotoin RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 1.0mg per mL.To 5.0mLof this solution add 5.0mLof Internal standard solution,and mix.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 100mg of ethotoin,to a 100-mLvolumetric flask.Add 75mLof Mobile phase,shake vigorously for 60minutes,dilute with Mobile phaseto volume,mix,and filter.To 5.0mLof the filtrate add 5.0mLof the Internal standard solution,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 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the resolution,R,between the analyte and internal standard peaks is not less than 2.0,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50µL)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 0.5for ethotoin and 1.0for ethylparaben.Calculate the quantity,in mg,of C11H12N2O2in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Ethotoin RSin the Standard preparation,and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.