Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 2: 100 rpm.

Time: 60 minutes.

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

Procedure— Determine the amount of C11H12N2O2 dissolved from UV absorbances 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 the Standard solution.

Tolerances— Not less than 80% (Q) of the labeled amount of C11H12N2O2 is dissolved in 60 minutes.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (3:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

Assay preparation— Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of ethotoin, to a 100-mL volumetric flask. Add 75 mL of Mobile phase, shake vigorously for 60 minutes, dilute with Mobile phase to volume, mix, and filter. To 5.0 mL of the filtrate add 5.0 mL of the Internal standard solution, and mix.

Chromatographic system (see Chromatography 621)—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 1.5 mL per 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 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.5 for ethotoin and 1.0 for ethylparaben. Calculate the quantity, in mg, of C11H12N2O2 in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Ethotoin RS in the Standard preparation, and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.