0.05M Tris buffer— Dissolve 60.5g of tris(hydroxymethyl)aminomethane in 6liters of water.Dilute with water to 10liters,and adjust with phosphoric acid to a pHof 9.0±0.05.Dissolve 100g of sodium lauryl sulfate in about 6liters of the prepared buffer,transfer this solution to the remaining buffer solution,and mix.

Medium:0.05M Tris buffer; 900mL.

Apparatus 2: 100rpm.

Time: 120minutes.

Triethylamine solution ,Mobile phase,and Chromatographic system—Proceed as directed in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Phenytoin RSin methanol to obtain a solution having a known concentration of 3.0mg per mL.Transfer a portion of this solution to a suitable container,and dilute quantitatively,and stepwise if necessary,with Dissolution Mediumto obtain a concentration of 0.06mg per mL.Transfer 10.0mLof this solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Test solution— Withdraw a portion of the solution under test,and filter,discarding the first 3mLof the filtrate.Pipet 10.0mLof this solution into a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Procedure— Separately inject equal volumes (about 25µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the areas of the peak responses.Determine the amount of C15H12N2O2dissolved by comparison of the peak responses obtained from the Standard solutionand the Test solution.

Tolerances— Not less than 70%(Q)of the labeled amount of C15H12N2O2is dissolved in 120minutes.

Triethylamine solution— Transfer 1mLof triethylamine to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Mobile phase— Prepare a filtered and degassed mixture of water,methanol,acetonitrile,Triethylamine solution,and acetic acid (500:270:230:5:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Phenytoin RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 0.5mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 250mg of phenytoin,to a 500-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency is not less than 6500theoretical plates,the tailing factor is not more than 1.5,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 25µL)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 C15H12N2O2in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Phenytoin RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.