A: Dissolve about 300mg of Phenytoin Sodium,accurately weighed,in about 50mLof water in a separator.Add 10mLof 3Nhydrochloric acid,and extract with three successive portions,measuring 100,60,and 30mL,respectively,of a 1in 2mixture of ether and chloroform.Evaporate the combined extracts,and dry the residue of phenytoin at 105for 4hours:the IRabsorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Phenytoin RS.

B: It responds to the flame test for Sodium á191ñ.

Mobile phase,Standard stock preparation,System suitability stock solution,and System suitability solution— Prepare as directed in the Assay.

Standard solution— Dissolve accurately weighed quantities of benzophenone,USP Phenytoin RS,USP Phenytoin Related Compound A RS,and USP Phenytoin Related Compound B RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having known concentrations of 0.5µg per mL,1µg per mL,9µg per mL,and 9µg per mL,respectively.

Test solution— Use the Assay stock preparation.

Chromatographic system (see Chromatography á621ñ)—Proceed as directed in the Assay,except to only use the System suitability solutionto evaluate the system suitability requirements.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the percentage of phenytoin related compound A,phenytoin related compound B,and benzophenone in the portion of Phenytoin Sodium taken by the formula: in which Cis the concentration,in µg per mL,of the respective analyte in the Standard solution;Dis the concentration,in µg per mL,of Phenytoin Sodium in the Test solution;and riand rSare the peak responses for phenytoin related compound A,phenytoin related compound B,or benzophenone obtained from the Test solutionand the Standard solution,respectively:not more than 0.9%each of phenytoin related compound Aand phenytoin related compound Bis found,and not more than 0.1%of benzophenone is found.Calculate the percentage of every other impurity in the portion of Phenytoin Sodium taken by the formula: in which Cis the concentration,in µg per mL,of USP Phenytoin RSin the Standard solution;riand rSare the peak responses of each impurity obtained from the Test solutionand the Standard solution,respectively;and the other term is as defined above.Not more than 0.9%of total impurities is found,excluding benzophenone.

Solvent— Use dimethyl sulfoxide.

Mobile phase— Prepare a filtered and degassed mixture of 0.05Mmonobasic ammonium phosphate buffer,adjusted to a pHof 2.5with phosphoric acid,acetonitrile,and methanol (45:35:20).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard stock preparation— Transfer about 100mg of USP Phenytoin RS,accurately weighed,to a 100-mLvolumetric flask,dissolve in Mobile phase,and sonicate,if necessary,to dissolve.

System suitability stock solution— Transfer 5.0mLof the Standard stock preparationto a 50-mLvolumetric flask,and dilute with Mobile phaseto volume to obtain a solution having a known concentration of about 100µg per g.

System suitability solution— Prepare a solution in 10mLof methanol containing 1.5mg of benzoin per mL,dilute with a mixture of 0.05Mmonobasic ammonium phosphate buffer,previously adjusted to a pHof 2.5with phosphoric acid,and acetonitrile (45:35)to volume.Transfer 1.0mLof the solution so obtained to a 10-mLvolumetric flask,and dilute with the System suitability stock solutionto volume.

Standard preparation— Transfer 5mLof the Standard stock preparationto a 100-mLvolumetric flask,and dilute with Mobile phaseto volume.

Assay stock preparation— Transfer about 100mg of Phenytoin Sodium,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.

Assay preparation— Transfer 5.0mLof the Assay stock preparationto a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Chromatographic system— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 0.6%.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the column efficiency is not less than 9960theoretical plates;the tailing factor is not more than 1.5;and the relative standard deviation for replicate injections determined from the benzophenone peaks is not more than 7.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak responses for the major peaks.Calculate the quantity,in mg,of C15H11N2NaO2in the portion of Phenytoin Sodium taken by the formula: in which Cis the concentration,in mg per mL,of USP Phenytoin RSin the Standard preparation;274.25and 252.27are the molecular weights of phenytoin sodium and phenytoin,respectively;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.