Medium: water;500mL.

Apparatus 2: 75rpm.

Time: 60minutes.

Procedure— Determine the amount of C12H14N2O2dissolved by employing UVabsorption 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 a Standard solution having a known concentration of USP Mephenytoin RSin the same Medium.

Tolerances— Not less than 70%(Q)of the labeled amount of C12H14N2O2is dissolved in 60minutes.

Mobile phaseand System suitability solution— Proceed as directed in the Assayunder Mephenytoin.

Test preparation— Use the Assay preparation.

Chromatographic system— Proceed as directed in the Assayunder Mephenytoinexcept to use a 225-nm detector.

Procedure— Inject a volume (about 10µL)of the Test preparationinto the chromatograph,record the chromatogram,and measure the peak responses.Calculate the percentage of each impurity in the portion of Tablets taken by the formula: in which Fis the relative response factor and is equal to 1.16for any peak with a relative retention time of 0.66,0.37for propiophenone,and 1.0for all other peaks;riis the peak response for each impurity;and rsis the sum of the responses of all of the peaks,adjusted for the relative response factor:not more than 1.0%of any individual impurity is found,and not more than 2.0%of total impurities is found.

Mobile phase,System suitability solution,Standard preparation,and Chromatographic system— Proceed as directed in the Assayunder Mephenytoin.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an amount of powder,equivalent to about 500mg of mephenytoin,accurately weighed,to a 100-mLvolumetric flask,add about 60mLof Mobile phase,sonicate for 10minutes,and shake by mechanical means for 30minutes.Dilute with Mobile phaseto volume,mix,and filter,discarding a suitable portion of the filtrate.

Procedure— Separately inject equal volumes (about 10µL)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 mephenytoin (C12H14N2O2)in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Mephenytoin RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.