A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

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

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

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

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into 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 CS is the concentration, in µg per mL, of USP Methsuximide RS in the Standard solution; CU is the concentration, in mg per mL, of Methsuximide in the Test solution; ri is the peak response for each impurity obtained from the Test solution; and rS is 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.

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (11:9). Make adjustments if necessary (see System Suitability under Chromatography 621).

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

Assay preparation— Transfer about 120 mg of Methsuximide, accurately weighed, to a 200-mL volumetric flask, dissolve in and dilute with Mobile phase to 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 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 5800 theoretical 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 20 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 C12H13NO2 in the portion of Methsuximide taken by the formula: in which CS is the concentration, in mg per mL, of USP Methsuximide RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.