Medium: water; 500 mL.

Apparatus 2: 75 rpm.

Time: 60 minutes.

Procedure— Determine the amount of C12H14N2O2 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 257 nm 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 RS in the same Medium.

Tolerances— Not less than 70% (Q) of the labeled amount of C12H14N2O2 is dissolved in 60 minutes.

Mobile phase and System suitability solution— Proceed as directed in the Assay under Mephenytoin.

Test preparation— Use the Assay preparation.

Chromatographic system— Proceed as directed in the Assay under Mephenytoin except to use a 225-nm detector.

Procedure— Inject a volume (about 10 µL) of the Test preparation into 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 F is the relative response factor and is equal to 1.16 for any peak with a relative retention time of 0.66, 0.37 for propiophenone, and 1.0 for all other peaks; ri is the peak response for each impurity; and rs is 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 Assay under Mephenytoin.

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

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of mephenytoin (C12H14 N2O2) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Mephenytoin RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.