A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

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

Test preparation— Use the Assay preparation.

Chromatographic system— Proceed as directed in the Assay 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 Mephenytoin 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 1.5% of total impurities is found.

Solvent: dimethyl sulfoxide.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed mixture of water, methanol, and acetonitrile (52:38:10). Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability solution— Transfer about 7.5 mg of propiophenone, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix. Transfer 1.0 mL of this solution to a 10-mL volumetric flask, add about 15 mg of Mephenytoin, dissolve in Mobile phase, sonicate, dilute with Mobile phase to volume, and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Mephenytoin RS in Mobile phase, sonicate, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 5.0 mg per mL.

Assay preparation— Transfer about 125.0 mg of Mephenytoin, accurately weighed, to a 25-mL volumetric flask, dissolve in Mobile phase, sonicate, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 257-nm detector and a 3.9-mm × 15-cm column that contains packing L7. The flow rate is about 1 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 1.0 for mephenytoin and 1.5 for propiophenone; the column efficiency is not less than 4000 theoretical plates for the mephenytoin peak; and the relative standard deviation for replicate injections for the mephenytoin peak is not more than 2.0%.

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 C12H14N2O2 in the portion of Mephenytoin 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.